
I had my first mix up with diesel and petrol (gas) yesterday.  I put petrol into a diesel van.  That's a no-no.  Lucky for me, I was still able to drive away from the gas station.
I was on my way back to the rental car agency and needed to just top off the tank.  It probably wasn't a good idea to pull into the gas station a 7am, knowing that I needed to have my wits about me to know whether to use the green pump or the black pump.  However, I'll maintain that it wasn't my fault.  I shouldn't have had to return the rental yesterday.  However, the rental car company screwed up my reservation.
I was supposed to have the van for 7 weeks, but the booked for only 4 weeks.  So I was returning the van only so I could go across the road and rent a car from their competitors for the remaining 3 weeks.  Apparently in Ireland, there's a tax law that states any rental over 28 days is considered a lease.  Leases are taxed at a higher rate and the cars have to be specifically classed as "lease" vehicles.  So despite the fact that I reserved a van with this company for 7 weeks, they put me in a rental-qualified (not lease-qualified)  vehicle.  Therefore, I needed to return the van after 4 weeks.  Additionally, I couldn't rent another car from them (return one, take out another) because both cars would have to qualify as "lease" vehicles.  If either one is a "rental" I was screwed.  The only one they had available for me was a "rental," so I was screwed.  Thus I reiterate, it was their own damn fault . . . OK, not really.  I was half-awake, uncaffeined and perturbed that I had to return the car.  Yet, I was still a dumbass.
The funny thing is that I didn't even realize that I had made the mistake until 8 hours later.  I slowly remembered over the course of the day that I used petrol, not diesel.  My inner monologue went something like this:  "Did I use diesel? Yeah, I think I did.  But it WAS making some odd noises.  Perhaps I didn't use diesel.  But I thought that if you used petrol in a diesel car it wouldn't start?  Maybe since I just topped off, it was still diesel-ly enough to start and drive, but gas-y enough to cause the odd rattling sounds.  Hmmmm . . . I think I used gas."
My next inner monologue was about what to do:  "Perhaps they won't notice?  But what about the next renters will they have an issue?  How much will this cost me?  Shit  It's gonna cost me, but I need to tell them."  So I called them.
Them:  "Hello, __________ rental cars."
Me: "Yeah, I returned a car today and . . . . uhhhh . . . I think I filled it with petrol . . . ."
Them:  "The ____________"
Me: "Yeah."
Them: "Yes, you filled with petrol.  We're draining the tank now."
Me:  "Sorry about that."
They seemed pretty cool about it, but being cool about it doesn't translate into "No charge, sir."  I figure I owe them at least a tank of gas - even at exhorbinant car rental agency prices.