In 1905, King Edward VII granted a Royal Warrant to the company for the supply of 'Pratt's Perfection Motor Spirit', and there were some 3,500 sales agents around the country offering the company's wares.

By the start of the First World War in 1914 the company was importing 14 million gallons of fuel per year to the UK, though sales of lamp oil would continue to exceed those of motor fuel until two years later.

Following the war, Anglo-American became the first in the UK to install a kerbside petrol pump - at Hale in Cheshire.

In 1925 Anglo-American acquired control of the British-Mexican Petroleum Co. Ltd, which included 10 storage and bunkering plants, a large fleet of motor lorries and eight 10,000 gallon distribution tankers.

The following year, the Esso brand was launched in the United States, but it would not be introduced in the UK until 1934. However, all the company's fuel brand names were changed to Esso within a year - the Pratt's brand name remained in use for lubricant products until the 1950s.

In 1938, Anglo-American began production at the UK's first oil well in Dalgeith, Scotland, which produces 10-20 barrels a day.

At the start of the Second World War, the company's tanker fleet was requisitioned by the UK Government to maintain fuel supplies to the UK. More than 350 employees died at sea during the war and by the war's conclusion only 15 Esso vessels remained. The company's Purfleet terminal on the east coast of England suffered considerable bombing damage during hostilities, but was never out of action for more than two weeks at time. Operation PLUTO ('Pipeline Under The Ocean') supplied petroleum from the Anglo-American refinery at Fawley for the D-Day landings.

In 1949 major construction work began at Fawley to create the UK's largest refinery. Two years later, on 14 September 1951, Prime Minister Clement Atlee officially opened the new Fawley Refinery, which was processing 124,000 barrels of crude oil per day within a year. A petrochemicals plant was constructed alongside the refinery and began operations in 1958.