There are few rather important differences between Russian and US oligarchies

As a matter of fact, there are some not easily discredited differences between Russian and American oligarchies. The wealth of the former is still largely perceived as being criminal and illegitimate. In contrast, many Americans admire their rich, and some famous US rich people created their companies from the bottom up instead of just seizing them and expropriating them from the people or the state. 

Moreover, Russian oligarchy came about as a result of the defeat of the Soviet Union thanks to the betrayal of many of these very current oligarchs who once were in or part of the late Soviet leadership. Communists turned oligarchs/capitalists are not quite the same as "pure breed" oligarchs or actual entrepreneurs becoming oligarchs. 

US oligarchy assimilated hundreds, if not thousands of years, of political cleverness of the masters. Russian oligarchs are new comers. US oligarchy is also the one which enjoys the spoils of the victor in the Cold War. 

The establishment of the Empire, US oligarchy, is based on numerous or almost countless institutions that is picking and buying global talents and brains. Russian oligarchy, on the other hand, put a new spin on wasting and neglecting the non-oligarchic "material"--people outside of the progressively more exclusive oligarchic circles or "social capital." 

To sum up, American oligarchy is like a established elite fraternity the "pledges" of which Russian oligarchs became (or so they were told or they were so promised) provided that they sell themselves and their country (and allies and friends) down the river. In this regard, for much of the "pledge period" from the 1980s till today, Russian oligarchy has been kept "sightless and led down flights of steps into a silent crypt, and helped into a coffin ..." But whether this is a true initiation leading to a full membership or just a devilish joke and mocking at the expense of an outsider/intruder/ is entirely at the pleasure and whim of the big masters.

Russian oligarchs are in relation to US oligarchs like Judases to the Romans.