Just want to add, to make it absolutely clear, I'm not against taking a nice rental car for a spin. As a matter of fact, I've done just that myself when the rental fairy has been particularly benevolent. But the longest detour I've ever taken is in the vicinity of 60 miles or so, which I find is financially and ethically acceptable. Racking up 3K miles and sending the bill to the company is certainly not, and if you were my employee you'd do that only once - the second time you wouldn't be in my employ anymore. Oh, and I'd never have signed your expense form, leaving you to foot the bill yourself for your idiotic stunt.