Online Casino Slots: A Guide to Types, Features, and Popular Games

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Online casino slots have become one of the most popular forms of online gambling, with thousands of different games available to players. In this article, we’ll explore the history of slot machines, the types of paying mechanics and bonus features found in online slots, the different types of jackpots, and the top 10 most popular online slots and vendors.

Online slots are digital versions of the traditional slot machine games found in brick-and-mortar casinos. These games typically feature three or five reels with various symbols on them, and players must match these symbols in specific combinations to win payouts.

In this article, we’ll take a closer look at the different types of online slots available, including their history, paying mechanics, bonus features, and jackpots. We’ll also provide a list of the top 10 most popular online slots and vendors, as determined by player popularity and industry reputation.

History of Slot Machines and their way to online casino

Invention and development of the first slot machine

The first slot machine was invented in 1895 by a man named Charles Fey. This machine featured three reels with five symbols on each, and players would win payouts by matching three of the same symbols on a single payline. Over the years, slot machines evolved to include more reels and symbols, as well as various bonus features.

Popularity of slot machines in the 20th century

Slot machines became hugely popular in the 20th century, with casinos around the world featuring rows upon rows of these games. As technology improved, slot machines became more advanced, incorporating features like video screens, touchscreens, and random number generators.

With the rise of the internet, slot machines made the transition to the digital world. Online slots offer players the convenience of being able to play from anywhere with an internet connection, as well as access to a wider range of games.

Types of Paying Mechanics


Betlines are the most common type of paying mechanic in online slots. These are horizontal or diagonal lines that run across the reels, and players must match symbols on these lines to win payouts.


Betways are similar to betlines, but they can run in multiple directions across the reels, increasing the number of potential winning combinations.


Megaways slots feature a random number of symbols on each reel, which can result in a huge number of potential winning combinations.

Cluster Pays

Cluster Pays slots require players to match symbols in clusters rather than on specific paylines.

Other paying mechanics

Some online slots use unique paying mechanics, such as split symbols or sliding symbols, to create more ways for players to win.

Bonus Features in Online Slots

Online slots are not just about spinning reels and hoping for a winning combination. Bonus features are what make them exciting and rewarding. Here are some of the most popular bonus features you’ll find in online slots:

Free Spins

this is the most common bonus feature in online slots. It allows you to spin the reels a set number of times without placing a bet, and any winnings you make during the free spins round are added to your balance.


in this bonus feature, you get to pick from a selection of items on the screen, each of which has a hidden prize. The prize can be cash, free spins, or other bonus features.

Cascading Reels

In this feature, winning combinations disappear from the reels, allowing new symbols to fall into their place. This can create multiple winning combinations from a single spin.


These are bonus features that multiply your winnings by a set amount. For example, if you get a 2x multiplier, your winnings will be doubled.

Other bonus features

There are many other bonus features in online slots, including wild symbols, sticky symbols, expanding symbols, and more.

Types of Jackpots in Online Slots

One of the most exciting things about playing online slots is the chance to win big jackpots. Here are the different types of jackpots you’ll find in online slots:

Progressive Jackpots

These are jackpots that grow every time someone plays the slot machine. A small percentage of each bet goes towards the jackpot, so it can grow very quickly. When someone wins the jackpot, it resets to a base amount and starts growing again.

Non-Progressive Jackpots

These are jackpots that have a fixed amount that doesn’t change no matter how many people play the slot machine.

Pooled Jackpots

These are jackpots that are connected to a network of slot machines. Every time someone plays one of the machines in the network, the jackpot grows.

Other jackpot types

Some online slots have unique jackpot features, such as mystery jackpots or community jackpots. Mystery jackpots are randomly triggered, and community jackpots are shared between players who are playing the same slot machine.

Top 10 Most Popular Online Slots

Slot NameVendorPaylinesRTPVolatilitySpecial Features
StarburstNetEnt1096.10%LowExpanding Wilds
Mega MoolahMicrogaming2588.12%HighProgressive Jackpot
Gonzo’s QuestNetEnt2095.97%MediumAvalanche Reels
Book of DeadPlay’n GO1096.21%HighFree Spins
Thunderstruck IIMicrogaming24396.65%MediumFree Spins
Immortal RomanceMicrogaming24396.86%HighWild Desire Feature
BonanzaBig Time Gaming117,64996.00%HighMegaways
Twin SpinNetEnt24396.55%MediumTwin Reel Feature
Dead or Alive IINetEnt996.82%HighSticky Wilds
Jammin’ JarsPush GamingCluster96.83%HighCascading Reels
Most popular Online slots

Note: RTP stands for Return to Player percentage and is a measure of how much a slot machine pays out to players over its lifetime. The higher the RTP, the more likely a player is to win back their money over time. 

Volatility is a measure of how risky a slot machine is, with low volatility slots paying out more frequently but with smaller wins and high volatility slots paying out less frequently but with larger wins.

When it comes to the most popular online slots, there are some that stand out above the rest. These games have proven to be a hit with players around the world, thanks to their exciting gameplay, engaging themes, and big win potential. Here are the top 10 most popular online slots:


Developed by NetEnt, Starburst is a classic slot that’s loved for its simple yet captivating gameplay. With expanding wilds and re-spins, players can rack up some big wins on this space-themed game.

Mega Moolah

This progressive jackpot slot from Microgaming is known for its massive payouts, which can reach into the millions. The safari theme and exciting bonus features make Mega Moolah a perennial favourite among online casino players.

Gonzo’s Quest

Another NetEnt classic, Gonzo’s Quest is a popular slot that follows the adventures of a Spanish conquistador. With avalanche reels and a free spins feature, Gonzo’s Quest is a high-variance game that can pay out big.

Book of Dead

Developed by Play’n GO, Book of Dead is an Egyptian-themed slot that’s become a hit with players thanks to its free spins feature and expanding symbols. This game has a high RTP and can offer some impressive payouts.

Thunderstruck II

Based on Norse mythology, Thunderstruck II from Microgaming is a sequel to the popular Thunderstruck slot. With 243 ways to win and a range of bonus features, including free spins and multipliers, Thunderstruck II is a great choice for players looking for big win potential.

Immortal Romance

This Microgaming slot has a vampire theme and features an engaging storyline that unfolds as you play. With multiple bonus features, including free spins and wilds, Immortal Romance has become a cult favourite among online casino players.


Developed by Big Time Gaming, Bonanza is a high-variance slot that’s known for its Megaways pay mechanic. With up to 117,649 ways to win and cascading reels, Bonanza can offer some massive payouts.

Twin Spin

This NetEnt slot has a retro feel, with classic symbols like bars and sevens. The unique feature of Twin Spin is that every spin starts with identical, adjacent twin reels that can expand to become triplet, quadruplet, or even quintuplet reels, leading to big win potential.

Dead or Alive II

Another NetEnt classic, Dead or Alive II is a Western-themed slot with a high-variance gameplay. With multiple bonus features, including free spins and multipliers, Dead or Alive II can offer some big win potential.

Jammin’ Jars

Developed by Push Gaming, Jammin’ Jars is a colourful and entertaining slot that features cascading reels and a free spins feature. With a maximum win potential of 20,000x your bet, Jammin’ Jars is a game that can offer some truly massive payouts.

Top 10 Most Popular Online Slot Vendors

In addition to the types of online slots available, the vendor that creates the slot games can also play a big role in their popularity. Here are the top 10 most popular online slot vendors:


NetEnt is one of the top providers of online slot games, known for their visually stunning and innovative titles.


With over 20 years of experience in the industry, Microgaming is a leading software provider of online slots and progressive jackpots.


Playtech is a well-known software provider of online casino games, offering a variety of slot games with high-quality graphics and exciting features.


Betsoft is a leading provider of 3D slot games with cinematic graphics and engaging storylines.


GT is a global gaming company with a focus on creating innovative slot games and progressive jackpots.


Yggdrasil is a newer software provider that has quickly gained popularity with their visually stunning and unique slot games.


Quickspin is a Swedish-based software provider that specializes in creating high-quality and innovative slot games.

Play’n GO

Play’n GO is a software provider with a focus on creating mobile-friendly slot games with engaging bonus features.

Red Tiger Gaming

Red Tiger Gaming is a leading software provider of online slots with high-quality graphics and exciting bonus features.


Novomatic is a global gaming company that specializes in creating land-based and online slot games with popular themes and engaging features.


In conclusion, online slots have come a long way since the invention of the first slot machine over a century ago. Today, players have access to a wide variety of slot games with different types of paying mechanics, bonus features, and jackpot types. The top 10 most popular online slots and vendors are a testament to the quality and innovation of the industry.

As online casinos continue to grow in popularity, we can expect to see even more exciting and unique slot games in the future. Whether you’re a seasoned player or new to online casinos, there’s never been a better time to try your luck on the reels.

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