I mean... if they neither "defects" (leading, potentially, to lack of supply for the other) and bids higher, they're benefiting from cheap fuel, right? Seems like they still sorta win, the only cost of abiding is that if they raised their bids they might be able to buy more of their overall fuel consumption at a higher (but still below-the-rest-of-the-market) rate, probably amounting to little further savings (and maybe none—if all major buyers defect and offer to pay more, the price of Russian fuel would approach that on the rest of the market). They can secretly hand-shake with one another on sticking to the cap, and just not say so publicly, leaving their options open. Doesn't seem like much of a sacrifice on their part, they'd have to really want to give "the West" the middle finger to not abide by the cap, I'd think.