United Airlines' non-Extended Range Boeing 777-200s have 364 seats in an economy-heavy, premium-light configuration.
They are used on high-capacity, short- to medium-range leisure routes.
Los Angeles-Honolulu, Chicago O'Hare-Orlando, and Denver-Washington Dulles are the most-served routes in February.
United has 19 so-called 'domestic' Boeing 777-200s, based on ch-aviation information, although not all are active. They are the non-ER versions and the original 777 variant. Few of the medium-haul aircraft were produced and even fewer remain. United's non-ER aircraft have had more seats added over the years, changing their economics and use. (It is a shame the above photo was not in the new livery, but I like it.)