As anyone who has ever traded CDS (or any other OTC, non-exchange traded product) knows, when you have a short risk position, unless compliance tells you to and they rarely do as they have no idea what CDS is most of the time, you always mark the EOD price at the offer, and vice versa, on long risk positions, you always use the bid. That way the P&L always looks better. And for portfolios in which the DV01 is in the hundreds of thousands of dollars (or much, much more if your name was Bruno Iksil), marking at either side of an illiquid market can result in tens if not hundreds of millions of unrealistic profits booked in advance, simply to make one's book look better, mostly for year end bonus purposes. Apparently JPM's soon to be fired Bruno Iksil was no stranger to this: as Bloomberg reports, JPM's CIO unit "was valuing some of its trades at prices that differed from those of its investment bank, according to people familiar with the matter. The discrepancy between prices used by the chief investment office and JPMorgan’s credit-swaps dealer, the biggest in the U.S., may have obscured by hundreds of millions of dollars the magnitude of the loss before it was disclosed May 10, said one of the people, who asked not to be identified because they aren’t authorized to discuss the matter. "I’ve never run into anything like that,” said Sanford C. Bernstein & Co.’s Brad Hintz in New York. “That’s why you have a centralized accounting group that’s comparing marks” between different parts of the bank “to make sure you don’t have any outliers” .... Jamie Dimon's "tempest in a teapot" just became a fully-formed, perfect storm which suddenly threatens his very position, and could potentially lead to billions more in losses for his firm.