MOSCOW/LONDON/NEW DELHI, July 27 (Reuters) - A Liberian-flagged oil tanker set sail in May from Russia's Ust-Luga port carrying crude on behalf of a little-known trading company based in Hong Kong. The new players have shipped at least half of Russia’s overall crude and refined products exports of 6-8 million barrels per day (bpd) on average this year, turning the little-known companies collectively into some of the world's largest oil traders, according to Reuters calculations based on private information from the 10 trading sources and Eikon data. A source with one major Russian oil company said his company was prepared to deal with higher credit risks from buyers for the sake of having stable and rising oil exports