1Sell orders at above-market price wouldn't be matched though, so you probably mean buy-orders? Please separate your answer into an answer post. It is alright to answer your own question, but please don't answer it in the question as it is impossible to vote on the answer that way. Could you please also provide a better explanation where you are observing hourly price spikes? I have trouble seeing such a thing in the provided chart. – Murch – 2014-03-27T15:34:22.410

@Murch You really don't see the spikes? I don't think he is trying to answer his own question. – 4276 – 2014-03-27T15:57:50.670

I see spikes, I have yet to see that they are forming any pattern at all. Every matched order shifts the chart, so it would only be without spikes if there were no market activity at all. His question's title is "What is causing the spikes?" and his text is "I think it is a trading bot". How is he not answering his own question? – Murch – 2014-03-27T15:58:38.500

@fredsbend I don't see it too. I totally agree with Murch on all points, except that I found the answer (it really isn't one) of such low quality that I down voted. If the poster improves the question/answer, I will un-down-vote. – Jori – 2014-03-27T16:02:25.443

Okay, I think I understand now that OP means the downward spikes (sell-orders) happening roughly between x:21 and x:24 several times during the day, not every hour though. @AlexMillar: It would be grand if you could confirm/clarify what you mean. – Murch – 2014-03-27T16:09:51.717

Thanks @Murch. Yes, I was mistaken - I should have written "buy-orders." I'm surprised you can't see them on bitcoinaverage.com. Here is a screenshot of what I see: http://imgur.com/aKYaDvX

Alright, that is outright weird: This is what the chart looks like for me: http://i.stack.imgur.com/x3Xex.png

@Murch Now we know we are both right. I see something like the image Alex linked. I would bet Jori sees what you see. I wonder why we are seeing such different charts.