Is is most likely your oil seal. Clean the oil up and see if there are any cracks in the cover... but it is most likely Time to replace your
oil seal. They cost about 5 bucks. Check the shaft where it contacts tht seal to make sure it isn't scored (this involves removing the seal).
Look on the engine's flywheel cover and you will find the model/serial number. You can look up the part number at
www.partstree.com by the engine and model number. You don't have to buy the parts there, but they have great diagrams.
If you don't know how to replace the oil seal, just google "small engine oil seal replacement"