Assuming certain similarities between European and U.S. cars, it could be something as innocuous as a drip from the crankcase breather vent or a seep from the oil filter cartridge. However, the first thing to do is determine if it is actually engine oil. If you have a front wheel drive car, it could be oil from the transmission or it could be anti-freeze. If it's an older car it could be a leaking oil line connection. I realize this hasn't been a whole lot of help, but the idea is to find out exactly where it's coming from first... Good luck!