Dear Tom and Ray:

A friend and I took a trip in my car. The gasoline bill was $40. What percent should he pay when I consider wear and tear on my vehicle? How do I calculate the bill fairly? -- Ralph

TOM: He should pay whatever you guys agreed he would pay in advance. These things are best negotiated before you're 280 miles from the nearest Chat n' Chew, and have to ride back home in brooding silence.

RAY: On relatively short trips, people tend to split the fuel cost. If you were going to take the trip anyway, Ralph, you now would have someone to keep you company, someone to pay for half of the gas and maybe even share the driving. That works for everybody.

TOM: And if your friend was generous, he'd offer to buy lunch since you provided the car.

RAY: If it's a trip that you were not going to make on your own (where the two of you sat down and said: "Hey, let's go to Canada to taste their burritos. Whose car should we take?"), then you might agree in advance to split the cost of an oil change, or your friend might agree to pay for more of the fuel to make up for the wear on the tires, brakes and other things that wear out with use.

TOM: But, like most deals, if money is an issue you feel strongly about, discuss it before you hit the road. Or suggest that you take his car.