A few years ago I looked into the ecosystem of ads and what potential money there could be in it. I've tried ads now on regular web sites and incorporated in an Android gamle launched on Google Play to see what would pay out best.
First some lingo. Google AdSense is one of the big players and that is what I've used for web site ads. It's very easy to get started with and you basically just add some HTML to your site content and AdSense figure out appropriate content for the ad tailored for the visitor.
Here's a screenshot from my admin view of adsense.
In English you can see stats here for the chosen time period. The number of page views containing ads (19 891), the number of clicks on ads (53) and the Click Through Ratio (CTR 0.27%). The Cost Per Click (CPC 2:41 kr) is the average amount of money you earn for a click. The Revenue Per Thousand visitors (RPM 6:43kr) is an indication on the earnings in relation to visitors as well. Total revenue for these ads so far during the selected time period is 127:81 kr.
What can we say about this? First of all the ads displayed here are shown on a few sites, a tournament administration site called Rankington, a book shop site using Amazon affiliates as backend and this blog. The absolute majority of the traffic is derived from this blog. This helps when analyzing the values.
A CTR of 0.27% is as I understand it quite bad. It means less than 3 in 1000 visitors clicks on an ad. A quick survey shows that a good CTR should be around 2%. Some sites report as high as 8%. My theory is that such sites are very niched and people visiting have been looking for information that may be handed by ads. For example a fishing equipment blog will probably get good CTR if the ads concern fishing equipment.
When analyzing the traffic to this blog, most visitors are probably techy people looking for a solution for a problem since most traffic is originating from Google and Stack Overflow. Once they have found what they are looking for, ads will not concern them.
So my advice would be: If you intend to make money on ads, be tactical about what kind of web site your planning on creating.
So how about making money on ads in games? I've made a few games for Android but never expected anyone to pay for them so I added Google AdMob ads in the game just to see the outcome. My interest was whether the large games like Angry Birds actually can make a living on only ads and no buying price.
My most downloaded game Othello Legends was unfortunately removed from Google Play earlier this year due to me not having the rights to the name Othello. And the stats can only be shown for this year. But here's a hint of the ad success using AdMob.
Pretty bad. So if my CTR was bad for the blog, it's even worse here. It's expected to make almost only a tenth of the AdSense income. Ok, the ads are only placed when you start the game and enter the help section, so ones you play there are no ads bugging you, which I thought fair.
Well, I only added ads for fun to see how they perform. But being a serious studio trying to making a living on ads, you would need enormous traffic. I find it hard to believe anything but the really popular games could muster that.