The Buenos Aires and Pacific Railway (BA&P) (in Spanish: Ferrocarril Buenos Aires al Pacífico) was one of the Big Four broad gauge, 5 ft 6 in (1,676 mm), British-owned companies that built and operated railway networks in Argentina.
The original concession was awarded by the Argentine government in 1872 to John E. Clark for the construction of a railway from Buenos Aires to Chile. It was not until 1882, when the BA&P was registered as a joint-stock company in London, that Clark was able to take over the concession. Initially the new company only intended to build the section between Mercedes, in Buenos Aires Province, and Villa Mercedes in San Luis Province. From Mercedes the company planned to obtain access to the city of Buenos Aires over the Ferrocarril Oeste track. At Villa Mercedes it connected with the Ferrocarril Andino line that ran on to Mendoza and San Juan.
Work began on the line to Villa Mercedes in July 1882 and the line was opened on 8 October 1886. After a change of plan, the company applied for, and was granted, permission to build its own independent access to Buenos Aires and this 107 km extension between Mercedes and Palermo, near the centre of Buenos Aires, was opened on 20 March 1888.
When it was first completed, the new line provided the provinces of the Cuyo with a direct rail link to the federal capital, instead of the much longer route, via Villa María to Rosario and then by river steamer to Buenos Aires.
In 1898 the BA&P took over the British-owned company Villa Maria and Rufino Railway and a year later John Wynford Philips became chairman of the BA&P, a post he held until 1938. During this period the company developed into a regional amalgamation of companies and dependent lines reaching from Buenos Aires to the Andes and extending from San Juan to Bahía Blanca. In 1907 the Argentine Great Western Railway, which had long been a rival of the BA&P, was taken over.
The line between Buenos Aires and Valparaiso in Chile was finally completed when the link between Mendoza and Santa Rosa de Los Andes in Chile, built by the Transandino Railway company was opened in 1910.
In 1908 the BA&P acquired part of a building in Florida Street, in the centre of Buenos Aires, for offices. As a result the building became known as Edificio Pacífico and since 1990 has housed Galerías Pacífico, a well-known shopping arcade.
When the entire Argentine railway network was nationalised in 1948, during Juan Peron's presidency, the BA&P became part of the state-owned company Ferrocarril General San Martín.