Thanks, Brokenwave, for the update. Gasbuddy shows the metro Phoenix average for unleaded at $4.65/gal on 3/11, so saving $1.20/gallon topping off in Sonoyta (and paying in pesos) makes some sense these days. The price differences in these markets are fascinating. If you're paying in USD, you'll get clipped a little in the peso/dollar forex - ARCO in Penasco posts a 19/1 exchange and I saw a few Pemex stores post 18/1. I'm also curious how accurate the pumps are at dispensing the full liter/gallon that you're paying for. I've always been satisfied with the gas quality and have never had any issues with Pemex gas.