Stir sweetened condensed milk, half and half, and vanilla together in a bowl.
Pour into bowl of ice cream maker and freeze according to the maker's instructions.
In a separate bowl, stir peanut butter and vegetable oil together until smooth.
During the last couple of minutes of freezer, slowly drizzle the peanut butter into the ice cream while still churning.
Turn off machine. Pour ice cream into a container and place in a freezer for several hours or longer.