Any idea why it is happening to us?

Not just you...I've been experiencing this with image ads for ages...supposedly this should not happen however I see it every day on my trade directory site and there is plenty of inventory for G to choose from.

In my case these are text ads but still it's quite irritating. Any idea how to get things right except from simply removing one of the ad blocks?

If you see duplicate ads, it's supposed to mean there isn't enough inventory to fill your ad blocks. I know of no way to fix it without removing at least one block (which is what I do when I see dupes)

Actually, now that I can think of it, if you added some content that possibly increased the available number of contextually relevant ads, that might do it. Hard to judge till you try it, though, and you'd be walking a fine line between relevancy for the page and relevancy for the ads. Might be worth trying though, if you're adamantly opposed to removing ad blocks.

Many thanks for your opinion, netmeg.

The latter ad block has arrows that allow me to see more ads and more ads are shown. What is more, the ads displayed as secondary on the second block of ads are not dupes.

Does that mean, there are many more ads that could be displayed but they won't be displayed as they pay too little to Google (and me)?

If you see duplicate ads, it's supposed to mean there isn't enough inventory to fill your ad blocks.

It happens are times on my site, but it is never been because of not enough inventory. My niche has many advertisers.

What I sometimes do is to block the advert for a while. All depends on how good the advert/site is.

Your niche may have many advertisers, but that doesn't mean that they're all eligible to appear on your site (or that your site is eligible to run their ads) at the precise moment you see duplicate ads.

Some variables include (but are not limited to)

- advertiser excluding your site specifically or by category

- you excluding advertiser specifically or by category

- advertiser budget (cpc, cpm, daily budget, etc)

- advertiser competition

- advertiser quality score

- smart pricing

- site targeting

- Google figuring out the context of your site, and the advertiser being smart enough to convey the context of his ad

- shoe size

Ok, I just threw the last one in there. The point is, we can't know, but there are a *lot* of calculations that go on every time ads display on a page. Just because there are tons of advertisers in a niche doesn't mean any or all of them are available to show up on your site, or that your site is available to the advertiser at the exact time you are seeing duplicate ads.

netmeg, I disagree.
My site for instance, DOES have a lot of advertisers. They show up all over the site. It is a competitive market. I know for a fact that it isn't due to a lack of advertisers etc. It doesn't happen at the end of the day, or geo-targeting.

I see it as a glitch more than anything else. And I normally see it with a new advertiser rather than an existing/established advertiser.

I am not too bothered by it though as it rarely happens (that I notice) and I do not clutter my pages with adverts. So one here or there isn't a big deal :)

I see it as a glitch more than anything else.

Yep, I agree and I think it's only happening to me in the UK.

Fortunately for me the one advertiser I have this happening with has created a fabulous graphic ad for every type of ad block there is so they do look very professional.

This has been discussed here in the past and at one time an ASA asked anyone experiencing this to contact AdSense support. Of course that always entails (for some) the concern of calling of AdSense's attention to your site and some risk that things could go awry.

When I experience duplicate ads on a page (and it happens from time to time) I just ignore it and it goes away sooner or later.


FarmBoy

Yep, I agree and I think it's only happening to me in the UK.

No it is happening outside UK also.

One more possible reason is, in the adwords there is an option to show ads as frequently as possible.

AAAh... I think I just got the best possible reason for it.

Here is how I think...

While making adwords, suppose I have ad campaign 1, ad campaign 2, ad campaign 3.

Ad campaign 1 is for Mens Product
Ad campaign 2 is for Womens Product
Ad campaign 3 is for Kids Product

Suppose all the three have been adjusted for Max Bid. What happens...

In a particular site all the three ads will appear. First Mens, second Womens, and third Kids based on the bid.


Now suppose what would happen if I change the ad campaign in the following way...

Ad campaign 1 is for Mens Product
Ad campaign 2 is for Mens Product
Ad campaign 3 is for Mens Product

Now for Google, each is different from the other...

So in place of the earlier three different ads, the site sees three same ads while Google believes it as three different ads and shows it on the same page!

Hi netmeg,
many thanks for your patience :-) but all your reasons are about:
- the site is not good enough (advertisers excluded it or google does not send ads);
- ads are not good enough (advertisers have ads working too poorly).

On my pages I have two ad units:
- medium rectangle with 4 ads in it;
- a skyscraper with 5 ads in it;
Each ad unit has a possibility to see another 5 ads after clicking a right arrow. I can click the arrow many times. I just checked and the medium rectangle shows 5 sets of 4 ads. The skyscraper has another 5 sets of 5 ads available.
So there definitely are ads available. Just the system picks same ad to show on 2 "default" sets.
Who knows, maybe the system is right and this ad makes us (and the system) most money. Still, it was interesting to post it here.

We've seen this for years. In our case part of it has to do with a bug they have when you use one of the more obscure, but now approved (we were a beta tester), features of Adsense. I think nowadays it has more to do with what produces best on your site, appearances be d@mned. We have a number of pages with a 300x250 centrally and a 160x600 on the lower side and we look like the poster-child site for this certain company with HUGE VIBRANTLY COLORED olive green (not so attractive) full-size graphic ads showing up in both ad units at the same time (including on our home page. erg!

Seeing this now. Two ad units each with two ads. First one had ads A and B while the second had ads B and C.
Ad B is actually is the best match to the site's topic of any on any page so I am not complaining.