We have heard that speculators have been buying oil, and with the market in contango, actually taking delivery of oil so as to get the benefit of the price increase expected in future months. I would presume that this oil is not really in line to get refined (at least very quickly). Is there any chance that this oil is affecting the numbers?

That is a myth.
Speculators buy “paper barrels” through futures or options. They don’t really buy and store crude in tanks.
Also, the “non-commercial” net long positions are at present perfectly in line with the historical levels, so “speculators” are not accumulating oil, not even in “paper barrels”.

Besides, the storage levels of crude and processed derivatives are well known for the OECD, and they are at present at medium-low levels…
You can check them in the monthly Oil Market Reports of the IEA:
http://omrpublic.iea.org/archiveresults.asp?formsection=full+issue&formd...

I'd have to go find the ref, but I recall that there was an investment bank trading operation in NY that got involved with the cash market (storing crude in docked tankers) in order to enhance their trading operations -- to your point though, while this kind of thing may be true, people will magnify its significance beyond any sort of reason.