Hmm. I'm not sure exactly what aspect of the pronunciation is giving you trouble here. But I can say:
1). the "-l" after these vowels causes them to lengthen. Thus the vowel is "feel" is long: [fi:l]. The vowel in "feet" is noticeable shorter: [fit]
2). the word "oil" is very volatile in different American dialects. You might hear it pronounced [oil], [ɔil], [ɔ:l], [o:l] or something else. To a more limited degree, these same dialects with do the same thing with words like "foil", "coil", etc.
3). As far as the -l itself, it's pretty much like any other final l in English. It is not darkened nearly as much as it is in Britain, where you would hear "feel" as [fi:ɫ]
