In a heavy medium saucepan, bring water and oil to boiling. Stir in the uncooked long-grain rice. Cover and cook over low heat about 25 minutes or until liquid is absorbed.
In a small bowl, stir together the sugar, flour, and salt; set aside.
Add the milk, evaporated milk, and butter to rice in saucepan. Bring to boiling. Add the sugar mixture and stir until combined. Return to boiling.
Gradually stir about 1 cup of the hot rice mixture into the beaten egg yolks; return the egg-and-rice mixture to saucepan. Cook and stir for 2 minutes more. Stir in vanilla. Stir in raisins, if you like. Serve warm or chilled. Makes 10 servings.