Quote from Ghost of Cutten:
Regarding notions of BP going bankrupt - it is a UK-based multinational with ring-fenced US operations. Realistic worst case legally is the US assets get written down to zero. Reserves and revenues from the USA and Gulf of Mexico are about 1/3 of total BP activity. So that would be worth 1/3 of the market cap if they get sued into oblivion and lose the whole US/Gulf assets.
General S&P/oil-price decline and reputational knock-on effects outside N American maybe take it down to a 50% worst case loss of intrinsic value. Peak price was $60 so it's worth probably $30 as a conservative estimate (more if the legal issues get resolved), assuming it was not seriously overvalued at the peak.
Hence if you want value, you have to buy with sufficient margin of safety below $30. Personally I look for 50% discounts to conservative fair value, which means around $15 per share. Unless some other disaster occurs, I would see it as unlikely to have more than a 2-3% risk of permanent capital loss if you bought at those prices.
Remember that in late 2008/early 2009, pristine businesses with no problems sold for 50-75% discounts to fair value, and troubled businesses like LVS sold to probably 90% discounts to fair value. This time we don't have the same macro fears but it's quite possible that the stock falls 75% below its peak IMO. If you are less risk averse and more aggressive, I would say low 20s is about as high as it would be wise to pay.