My grandma was always getting stains out of our family's clothes when we were younger and this trick worked everytime.

You want to pretreat it by laying it flat and covering the stain with cornstarch. You want to let it sit there for atleast 30 minutes (depending on how bad the stain is). The cornstarch will soak up some of the oil (and you'll want to brush it away before washing). After it sat with the cornstarch, you should try soaking it in the sink with some Dawn dishwashing liquid using the hottest water you can. Soak it for a little while and then try squeezing it while its underwater until its been completely soaked up by soapy water. Then you'll want to rinse out the shirt to get out the majority of the soap. Then you'll want to use one of those pre-wash sprays like Oxyboost on the spot and then wash it on the regular cycle with some damp towells. Most of the time, the stain will be completely gone.