| Updated: September 26, 2025If you share our passion for games of chance, you probably enjoy spinning the reels as much as we do. On this page, the casino experts at BonusInsider focus on online slots and everything you need to know about them. We introduce you to the mechanics of slot machines and their components.
You can also learn about the biggest providers of online slot machines, as we present some of the hottest titles from NetEnt, Playtech, Yggdrasil, and Pragmatic Play – companies that continue to drive the remote gambling industry to new heights. All of these games are available for real money at BonusInsider’s recommended casinos, where you can also try them for free.
Our passionate slot experts explain the key features of the games you can play online. We discuss wilds, scatters, free spins, and bonus rounds, all of which can boost your chances of winning on the reels.
We help you distinguish between high-volatility and low-volatility slots so you know which type best suits your bankroll. We also take an in-depth look at one of the most important subjects related to spinning the reels and gambling in general: proper money management. Let’s get started by exploring the inner workings of a slot machine.
Main Components of Online Slots
Online slots operate in much the same way as their noisy cousins that dominate more than 80% of the floors in most land-based casinos. Here is the typical process when you play online: you deposit funds into your casino balance, open your preferred slot game, select your coin denomination and the number of credits you want to wager per round, and click the spin button.
You win when several identical symbols align in specific positions on the screen. If they do not, simply hit the button again and keep your fingers crossed, hoping that Lady Luck will be kinder to you on the next spin. Below are the main components that drive these enticing, money-sucking machines.
Reels
Paylines Paytable Coin Selectors Gamble Feature AutoplayReels
Reels are vertical columns of symbols that begin rotating when the player presses the spin button. The number of reels varies between games. Old-school slots feature only three reels, but there are also games with five, six, or even seven spinning reels. Many online slots utilize three rows of symbols, arranged in either a 5×3 or 3×3 reel grid.
The number of symbols per reel also varies from game to game. Players can calculate the number of possible combinations by multiplying the number of symbols each reel contains. For example, a slot with twenty symbols on each of its five reels yields 20 x 20 x 20 x 20 x 20 = 3,200,000 possible combinations, although not all of them result in a win.
Paylines
The paylines are components that most slots cannot do without. They indicate the positions in which matching symbols must align to produce a payout. The simplest slots have only one horizontal payline running across the middle of the reels. Today, the more sophisticated slots you can find online have multiple paylines that form a variety of patterns across the screen.
The more paylines there are, the higher your chances of collecting a payout. A slot player must bet one or more credits per line to activate it. Otherwise, the line will fail to produce a payout, even if matching symbols align to form the corresponding pattern. Some slots have a fixed number of paylines that you must play on each spin. Others allow you to deactivate some of the paylines, although this is clearly a bad idea because it reduces your chances of hitting winning combos.
Paytable
The paytable is the first thing you should check to determine whether a given slot is worth playing. It contains all the information you need about the game. This includes the paylines, bonus games, winning combinations with their respective payouts, and the direction in which identical symbols must align to yield a win. In the vast majority of online slots, matching icons must appear from the leftmost reel to the rightmost reel.
Coin Selectors
The coin selectors are the controls at the bottom of the game screen that allow slot players to adjust the amount they wager on each spin. They are easy to distinguish, although their design varies among slot vendors. You can recognize them by the +/- buttons used to increase or decrease your coin denomination.
Many online slots also enable you to adjust the number of coins you bet per active line. Suppose you play a game with 20 fixed paylines and can wager up to 5 coins at $0.50 per line; your total bet per spin would be $50.
Gamble Feature
Many online slots have a gamble feature that activates only after a winning spin. It gives players the opportunity to increase their winnings by playing a simple side game in which they must predict the color of a playing card’s suit to double their payout. In many games, you can even quadruple your winnings by correctly guessing the card’s exact suit.
Autoplay
Autoplay is one slot feature that players are advised to leave alone. When activated, it makes the reels go through a preconfigured number of rounds automatically. This spares you the effort of clicking the spin button, but it comes at a cost.
It causes you to play at a dangerous pace, which in turn brings you closer to the house edge of the slot. If you insist on using it, we suggest adjusting the settings so that the feature stops whenever your balance falls by an amount you can stomach. Otherwise, the autoplay feature may eat up your entire bankroll for the session.
Special Features of Online Slots
Today’s sophisticated slots are packed with all kinds of special features designed not only to boost your chances of pocketing a sizable payout but also to enhance the games’ entertainment value and interactivity.
Multiplier Symbols Scatter Symbols Wild Symbols Free Spins Bonus GamesMultiplier Symbols
Some slots feature symbols that multiply your winnings by a certain factor when they are part of a winning combination. These multipliers can have values such as 2x, 3x, 4x, 5x, and so on. If you land a combination with a 3x multiplier, your payout will be tripled.
In many newer games, players can benefit from progressive multipliers. However, these multipliers are not tied to specific symbols. A progressive multiplier is activated after a win and increases with each successive winning combination until it reaches its maximum value. Conversely, a losing spin resets the multiplier to its initial level.
Scatter Symbols
Scatter symbols are special in more than one way. In some games, these symbols yield payouts, but unlike regular icons, scatter symbols do not need to land on a payline to reward the player.
They pay out as long as matching symbols land in any position on adjacent reels. Another important function of scatter symbols is to trigger bonus games or free spins. Typically, several scatter symbols must appear on the reels to unlock a bonus.
Wild Symbols
Wild symbols are hugely popular among slot players, and for a very good reason. If you have played video poker variants like Deuces Wild or Joker Poker, you probably know what these symbols are all about. Similarly, they act as substitution icons that can stand in for all symbols except special ones – for example, a wild cannot replace a scatter.
It makes sense that the presence of these powerful substitution symbols improves your chances of forming winning combinations. Wilds may or may not award regular payouts, depending on the game. There are all kinds of wilds, including expanding, stacked, shifting, and sticky ones.
Free Spins
Free spins are another coveted feature in the reel-spinning community. Usually unlocked by landing three or more scatter symbols, they give players the opportunity to win without placing an additional wager.
Different games award a predetermined number of free spins. In some slots, the free spins can be retriggered with the same combination of symbols that unlocked them in the first place. Some free-spin rounds apply multipliers to any wins players generate during the feature. There are even slots where each winning combination adds to your initial tally of free spins.
Bonus Games
Bonus games are what make contemporary online slots so exciting. In some slots, these appear as pick-me games, where players must choose among various objects that conceal hidden cash prizes.
In others, you spin a wheel, and each section of the wheel awards a different cash amount. Not only are bonus games lucrative, but they also help hold players’ attention for longer, preventing them from getting bored quickly. Keep in mind that no skill whatsoever is involved in triggering bonus games. It all comes down to luck.
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Slot Variance
Variance (also known as volatility) denotes the level of risk inherent to a certain slot. It tells you how much and how frequently you can expect to win or lose when playing a particular game. It should not be confused with the average return rate, though, because a low-variance slot can offer a high player return percentage and vice versa.
High-volatility slots yield long dry spells of losing spins, with a lower hit frequency of matching combinations. Here wins are less consistent in terms of frequency but when you do hit a winning combo, the slot rewards you generously for your persistence.
Low-volatility slots are practically the opposite of high-volatility ones. They offer more action as winning combinations here occur rather frequently but the payouts are within the low to mid-range in terms of size. The frequent albeit smaller wins keep players intrigued and engaged in these low-risk games for a long time.
Recommended for players who have the time, patience, and bankrolls to survive long losing streaks. Such games may offer a good deal of excitement but are unsuitable for the faint of heart. Avoid them if you are underbanked or averse to risk.
Recommended for casual spinners who play for entertainment purposes only. They are also suitable for slot mavens with less sizeable bankrolls who are looking to play for longer periods of time.
Popular Slots
Major Slot Software Studios
The number of software providers offering quality slots to online casinos has been on the rise lately, driven by the enormous popularity these games enjoy. The slot experts at BonusInsider have hand-picked only the biggest and best vendors of online slot games. Below, you can learn about all the top-ranking slot software developers we recommend.
Microgaming NetEnt Playtech Yggdrasil Pragmatic Play Play'n GOMicrogaming
Microgaming is easily the largest supplier of premium slots in the world, with a catalog that comprises hundreds of distinct titles. The award-winning studio has more than 850 games in its portfolio and offers a minimum of two new slot releases each month. Here’s another interesting bit of trivia for you – Microgaming boasts the largest progressive slot network on the web, with more than $1 billion paid out in winnings to date.
NetEnt
NetEnt is another frontrunner in the gambling industry. The Swedish company was among the first software studios to develop and launch open-source games that rely on Java technology. Its instant-play slots have great appeal thanks to their high winning potential, captivating visuals, and extensive customization options. The supplier has a particularly strong presence in major European markets such as Sweden and the UK.
Playtech
The developers at Playtech share a deep passion for delivering the very best in casino gaming. The studio has created a wealth of outstanding slots since its inception in 1999. Today, Playtech offers its top-shelf slots to more than 140 licensed operators across 20 regulated markets.
Yggdrasil
Yggdrasil is one of the newer software studios, having launched operations in 2013. Despite its youth, the company is regarded as one of the most acclaimed suppliers of sophisticated 3D slots worldwide. The studio embraced HTML5 in 2014, ensuring cross-compatibility of its slots across all desktop and small-screen devices.
Pragmatic Play
Founded in 2015, Pragmatic Play can hardly be called a pioneer in the industry. Nevertheless, the studio has quickly established itself as a leading provider of casino software, thanks to top-rated slot titles such as Wolf Gold, Madame Destiny, Sweet Bonanza, and Hot Safari.
Play'n GO
Play’n GO boasts a range of more than 70 high-quality games, available in about 20 languages and nearly as many currencies. The studio designs its titles with mobile users in mind, utilizing both Flash and HTML5. Always at the forefront of innovation, Play’n GO recently launched Wild Rails, the first online slot to feature horizontal rather than vertical reels.