Not much history is available for the various early individual companies operating horse cars.
Alameda Oakland & Piedmont Electric Railroad - incorporated 1870, opened 1875, electrifed 1893, sold 1898 to Oakland Transit Co.
Berkeley Traction Co. - sold 1906 to Oakland Traction Co.
Central Avenue Railway - incorporated 1891, opened 1893, sold 1898 to Oakland Transit Co.
Claremont University & Ferries Street Railroad Co. - incorporated 1888, ceased operations in 1901 with some service later assumed by Oakland Transit Co.
Consolidated Piedmont Cable - incorporated 1891, sold 1895 to Piedmont & Mountain View Railway Co., sold 1898 to Oakland Transit Co.
East Oakland Street Railway - incorporated 1893, sold 1898 to Oakland Transit Co.
Highland Park & Fruitvale Railroad - opened 1878, electrified 1893, sold 1898 to Oakland Transit Co.
Oakland Consolidated Street Railway - incorporated 1890, acquired Oakland & Berkeley Rapid Transit Co. (incorporated 1891), sold 1898 to Oakland Transit Co.
Oakland Railroad - incorporated 1864, sold 1901 to Oakland Transit Consolidated Co.
Oakland San Leandro & Haywards Electric Railway Consolidated - incorporated 1894 consolidating Oakland San Leandro & Haywards Electric Railway and Twenty-Third Avenue Electric Railway Co, sold 1901 to Oakland Transit Consolidated Co.
Webster Street & Park Railway - sold 1904 to Oakland Traction Consolidated Co.
East Shore & Suburban Railway - incorporated 1906, operated between Oakland and Richmond, sold 1912 to San Francisco-Oakland Terminal Railways.
California Railway - incorporated 1890, sold 1912 to San Francisco-Oakland Terminal Railways.
San Francisco Oakland & San Jose Railway - incorporated 1902, opened 1903, merged with San Francisco & Bay Counties Railway in 1908 forming San Francisco Oakland & San Jose Consolidated Railway. Operated trans-bay service.
In 1895, Realty Syndicate was formed as a holding company, to begin consolidation of the local street railways in Oakland. In 1898, Realty Syndicate formed an operating company Oakland Transit Co., which would acquire the street railways. In 1902, Oakland Transit Co. was reorganized as Oakland Transit Consolidated Co., in 1904 as Oakland Traction Consolidated Co., and in 1906 as Oakland Traction Co. In 1912, Oakland Traction Co. was merged with the trans-bay San Francisco Oakland & San Jose Consolidated Railway, forming San Francisco-Oakland Terminal Railways. Although the local and the trans-bay systems continued to be operated separately. Sold in 1923 to Key System Transit Co., and sold in 1946 to National City Lines as subsidiary Key System Transit Lines. Acquired 1960 as publicly owned Alameda Contra Costa County Transit District.
The Key System services connecting the East Bay with San Francisco were generally operated separately from the local transit services. Trains connected with ferry boats until 1939, when the Key System began using the lower level of the newly opened Bay Bridge. In 1958, the lower level of the bridge was paved, and public transportation across the Bay was limited to buses until the 1974 opening of the Bay Area Rapid Transit (BART) tunnel underneath the Bay.
From 1939 until 1941, also using the Bay Bridge were trains of the Southern Pacific Railroad, a steam railroad which had electrified some suburban lines in 1911. After discontinuance, some routes transferred to the Key System.
And also from 1939 until 1941, also using the Bay Bridge was the Sacramento Northern Railroad interurban line. After discontinuance, replacement bus service operated by Pacific Greyhound Lines.