What is the rank of the petroleum company who has a revenue of $481.7 billion?
CREATE TABLE "fortune_2013_list" (
  "rank" real,
  "company" text,
  "country" text,
  "industry" text,
  "revenue_in_usd" text
);
SELECT MIN("rank") FROM "fortune_2013_list" WHERE "industry"='petroleum' AND "revenue_in_usd"='$481.7 billion';