Officers from the canton force came across the apparently abandoned car on the shoulder of the road on Friday and found it was unlocked, police said in a news release.
A routine search of the vehicle, with a licence plate from outside the canton, uncovered 100,000 francs ($98,000) in cash, the release said.
Police found the money in an open envelope in the doormat for the front passenger seat, stuffed with 100-franc and 200-franc notes.
Apparently suspicious about the large sum of money in an unlocked car, officers contacted another patrol unit, which caught up with the owner of the vehicle walking along the side of the highway several hundred metres away.
The man acknowledged being owner of the car parked on the side of the road and informed police that he was attempting to get fuel after running out.
It seemed unusual that a man with so much cash would run out of petrol.
But an investigation by police found the man's statements were true.
It turned out he had a very good explanation for the cash in his car.
He had just been to a trustee's office, where he had received the money.
Police said they later learned he had just inherited 70- to 90-million francs ($69 million-to-$89 million).
Which may explain why the man was not paying attention to the petrol gauge in his vehicle, and perhaps why he was so absent-minded about not locking the car and leaving the tidy sum inside.
After all, what's 100,000 francs when you're about to inherit more than 700 times that sum . . .