The following table presents EMCOR's operating income, and operating income as a percentage of segment revenues, for the years ended December 31, 1999, 1998 and 1997 (in thousands, except for percentages):

Operating income increased for the United States electrical construction and facilities services operations for 1999 compared to 1998. The dollar increase in operating income for 1999 of $2.2 million, or 6.0%, as compared to 1998, was attributable to the incremental effect of businesses acquired during 1999 and 1998 as well as growth from the balance of EMCOR's operations. As a percentage of revenues, operating income decreased by 0.3% for 1999 as compared to 1998 primarily due to reduced operating income for certain operations which were only partially offset by a higher percentage of revenues being derived from markets where higher operating income margins are more typical than in other EMCOR markets, particularly in Eastern United States cities such as New York City, Boston and Washington, D.C. Operating income for 1998 for the United States electrical construction and facilities services operations increased $7.6 million, or 26.6%, from 1997 levels due to a similar increase in revenues for businesses operating in the Eastern United States, particularly in New York City due to renovation projects.

United States mechanical construction and facilities services operations operating income increased $16.9 million for 1999, an 80.5% increase over 1998 amounts primarily due to growth of EMCOR's existing businesses and operating income contributed by businesses acquired during 1999 and 1998. For 1998 compared with 1997, operating income increased $2.3 million, or 12.5%, primarily due to businesses acquired in 1998. As a percentage of revenues, operating income increased 0.3% from 1997 to 1998 and 0.1% from 1998 to 1999, principally due to the continued strong renovation market in New York City and new construction markets in Denver and Salt Lake City.

United States other operating losses decreased $0.4 million for 1999 as compared to 1998 primarily due to the continuing development of consulting and maintenance services operations, offset partially by incremental operating income from certain businesses acquired during 1999 and 1998. Operating losses for 1998 compared to 1997 increased by $2.7 million primarily due to costs associated with the development of the consulting and maintenance services activities.