Yeah, it's on Average, one Oil Well per 40 chunks. My comment was to show that it's not that you will have precisely one Oil Well per 40 chunks. I have found 5 Oil Wells who were less than 50 blocks apart from eachother, with the central oil spill being 30+ blocks high. All the others were the smallish common ones with 5 or 6 blocks above sea level. I also found another concentration of those smaller ones, 4 very close together, and several times in Oceans you see double oil spills. Not uncommon to see those 10+ rare ones, too. Oil is definitely plentiful in certain biomes, Ocean being the one with the highest concentration.
The way you worded it seemed to indicate that the Oil Wells only generated every 40 chunks, which would definitely make it a pain to obtain it, but that's not the case. While you can, naturally, spawn somewhere where there are absolutely NO Oil Wells for 100's of blocks in every direction, it's basically guaranteed by the Algorithm that as soon as you explore more, you will find these oil motherlodes. Which, you know, is the whole POINT of Oil. You search, and you search, and you search, until you finally get to those massive Oil spills that go 30+ blocks high in the air, and get you more than 4000 buckets worth of Oil, enough to last you for quite a while after you turn it into fuel. It's also always a good idea, to keep searching for more Oil Wells as you continue exploring, and marking the coordinates down so that you already know where to go later. Of course, most of the people who play FTB end up giving up Oil and going Biomass/Biofuel, because it's easier to automate and produce.
What this means is... Yes, it's sometimes a pain to get enough oil. But it was intended, so as to balance it. Mystcraft oil page... Not a terribly good idea. Someone already said that the world corruption is pretty high when you use it, which balances it to some degree, but personally, i really don't think it's enough... Infinite Oil, right off the bat... No pain involved.