Royal Dutch Shell:

Shell was vertically integrated and is active in every area of the oil and gas industry, including exploration and production, refining, distribution and marketing, petrochemicals, power generation and trading. It has minor renewable energy activities in the form of biofuels and wind. It has operations in over 90 countries, produces around 3.1 million barrels of oil equivalent per day and has 44,000 service stations worldwide. Shell Oil Company, its subsidiary in the United States, is one of its largest businesses.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". What is the name of Shell's subsidiary in the United States?
Shell Oil Company