Bacco Transit Co. - began operating in 1921 around Wilmerding.
Bamford Motor Coach Lines - based in Munhall, began operating in 1921.
Bigi Bus Lines - based in Bridgeville, began operating in 1922.
Brentwood Motor Coach Co. - based in Brentwood area. Formed in 1929, combining following two bus companies. Carrick & Bruceton Auto Bus Line began operating in 1911, renamed in 1917 to Carrick & Bruceton consolidated Bus Line. And in 1917, Antonio Maddalon began operating bus line between Broughton and Hillcrest.
Burrelli Transit Service - began operating in 1928 in Braddock. In 1949 acquired Miller Bus Co.
Carnegie Coach Lines - based in Carnegie. Formed in 1946, acquiring routes from Montour Motor Coach Lines.
Community Transit Service - formed in 1953, acquiring route from Penn Transit Co. between Pittsburgh and Avella, which had existed since 1920. In 1961, acquired routes from Harmony Short Line operating between Pittsburgh and New Kensington.
Culmerville Russellton & Cheswick Transit Co. - based in Cheswick, began operating in 1912. In addition, Culmerville Auto Transit Co. began operating in 1916, and Tarentum Auto Transit Co. began operating in 1914. Culmerville Auto Transit Co. later acquired Tarentum Auto Transit Co., and was acquired by Culmerville Russellton & Cheswick Transit Co. in 1958. In 1961, acquired routes from Harmony Short Line.
Dawson Motor Coach - began operating in 1927 in Braddock.
Debolt Transit Co. - based in Homestead. Began operating in 1949 by acquiring two routes from Bamford Motor Coach Lines.
Deere Brothers - based in Turtle Creek, began operating before 1925.
Duquesne Motor Coach Lines - based in Duquesne, replaced streetcars which had been operated by Duquesne & Dravosburg Railway Co. from 1910 to 1928.
J. M. Ferguson - served Ben Avon beginning in 1929.
Gradison Auto Bus Co. - based in Burgettstown, began operating in 1925. In 1953, acquired Montour Motor Coach Lines, which had been started in 1922 by John and George Sauers, sold to Montour Motor Coach Lines in 1944. Combined route network restructured in 1953, with some route segments transferred to Poskin Bus Lines. Remained independent until 1970, when routes finally acquired by Port Authority Transit.
Horrell Transportation Co. - based in Millvale area, began operating in 1936. In 1954, acquired Beaver Suburban Motor Coach, which had been formed in 1941, acquiring routes which had operated since 1938.
McCoy Brothers - based in Turtle Creek, acquiring route in 1921.
McKeesport Transit Co. - formed in 1929, acquiring Highland Grove Bus Co., which had replaced the Highland Grove Traction Co. This was an electric railway, which from 1898 to 1923 had operated northeast of McKeesport.
Mon Valley Bus Co. - based in Clairton. The Clairton Street Railway had operated streetcars since 1904, until abandonment in 1926. Clairton City Bus began operating 1923, acquired 1928 by newly formed Mon Valley Bus Co. A competing company, Clairton Bus Lines, began operating 1926, acquired 1943 by Mon Valley Bus Co. In 1948, Mon Valley Bus Co. sold to Noble J. Dick Lines, continuing to operate under same name.
New Kensington City Lines - formed in 1956 as separate subsidiary of Penn Transit Co., which in 1948 had acquired Westmoreland Transportation Co. Westmoreland Transportation Co. was formed in 1921, and in 1941 acquired local bus routes in New Kensington, which has been operated by New Kensington Taxi Cab Co. Streetcar service had operated in New Kensington since 1906, originally by Allegheny Valley Street Railway Co., which was acquired by West Penn Railways Co. in 1912. Streetcars were discontinued in 1937.
Ohio River Motor Coach Co. - based in Ambridge, began operating in 1936 between Pittsburgh and Aliquippa.
Oriole Motor Coach Lines - based in Mt. Lebanon area. Formed in 1928, acquiring operation started by John Collavo in 1919.
Penn Transit Co. - based in McKeesport. Formed 1925 as Penn Bus Lines, a subsidiary of West Penn Railways Co., renamed 1934 to Penn Transit Co. West Penn Railways Co. was formed in 1904, as a consolidation of various street railways and interurban railways in the area. Streetcars had operated in McKeesport since 1890, and operated until 1938.
Poskin Bus Line - based in McDonald. Formed 1933, acquiring routes from Penn Transit Co., which had existed since early 1920's.
Ridge Lines - based in McKeesport. Between 1905 and 1919, transportation between McKeesport and Port Vue was provided by Port Vue Street Railway. In 1922, Ben V. Rudberg began operating bus service between McKeesport and Port Vue, extended in 1937 to Liberty. In 1945, sold to Ridge Lines.
Roger's Transit - formed in 1961, acquiring route from Harmony Short Line, which had existed since 1940.
Schafer Coach Lines - based in Coraopolis. Formed 1937, acquiring route started in 1928 by Helsley and introducing additional routes.
Trafford Coach Lines - based in Trafford, began operating in 1941.
Wall Bus Line - began operating in 1934 between Wilmerding and Wall, having acquired route from McKeesport Transit Co.
William Penn Motor Coach Co. - began operating in 1952 between Pittsburgh and Monroeville.
Additional obscure bus companies previously existed, according to the 1952 "Mass Transportation's Directory", and the WPA American Guide Series of state guidebooks.