A colleague told me of a gas station that found after many years, that they had sold more gas than they had bought. Eventually they realized that it was because

A colleague told me of a gas station that found after many years, that they had sold more gas than they had bought. Eventually they realized that it was because their tanks were filled up at night, when gas was cooler/less voluminous than when it was pumped out in the heat of the day (it was in the central valley of CA, which gets very hot).