It operates in oil and gas in exploration and production, refining, transport, distribution and marketing, petrochemicals, power generation and trading, and is also engaged in renewable energies with biofuels, wind, and hydrogen. Website: shell.com – Market cap.: £ 148.6 Billion – Stock symbol: RDSA. Summary: Top 10 companies from the UK 2020 Top 10 most productive companies in the UK. Oil and gas explorer Soco is the “most productive” company in the UK, according to a major study. Arctic oil race heats up: Oil and gas explorer Soco is named the 'most productive' company. By Louisa Peacock.