The AP Stylebook recommends abbreviating the words “Company” and “Corporation” as Co. and Corp., respectively, when they appear at the end of a proper name, but not if the word occurs elsewhere in the name.
Ford Motor Co. Aluminum Company of America
Gulf Oil Corp. Corporation for Public Broadcasting
Subsequent references to “the company” or “the corporation” should be spelled out and not capitalized.
Quirky Car Co. came out with a new model, the Zoomer. The company believes this revolutionary “green” car will make gasoline obsolete.
The Perfidius Corp. was indicted for offering bribes to foreign countries to drill for oil. The corporation is also being sued by stockholders for fraud.
For plurals, Co. becomes Cos., as in American Broadcasting Cos.
For possessives, the thing belonging to the Co. becomes the Co.’s, and the thing belonging to the Corp. becomes the Corp.’s.
For plural possessives, the thing belonging to the companies becomes the Cos.’