Here's a thought: Could it be a form of weak lock-in? If you fill your tank on Monday, then you're less likely to fill up at that cheaper gas station on Thursd

Here's a thought: Could it be a form of weak lock-in? If you fill your tank on Monday, then you're less likely to fill up at that cheaper gas station on Thursday. When the next Monday comes around, you're probably going to need to fill up again, and well, there they are :)