Management’s Discussion and Analysis of Financial Condition and Results of Operations  (continued) f-6 | 7 Forrester Research | Annual Report 2000 Increases in total revenues and revenues from core research were primarily attributable to an increase in the number of client companies to 1,793 at December 31, 1999 from 1,271 at December 31, 1998, an increase in the sales organization to 153 employees at December 31, 1999 from 92 employees at December 31, 1998, and sales of additional core research to existing clients. No single client company accounted for more than 2% of revenues for the year ended December 31, 1999. Advisory services and other revenues increased 53% to $22.6 million in the year ended December 31, 1999 from $14.7 million in the year ended December 31, 1998. This increase was primarily attributable to increased demand for Forrester’s advisory services programs and Forum events, an increase in the number of events held to eight in the year ended December 31, 1999 from six in the year ended December 31, 1998, and an increase in research staff providing advisory services to 125 employees at December 31, 1999 from 97 at December 31, 1998. Revenues attributable to customers outside the United States increased 57% to $19.8 million in the year ended December 31, 1999 from $12.6 million in the year ended December 31, 1998. Revenues attributable to customers outside the United States increased as a percentage of total revenues to 22% for the year ended December 31, 1999 from 21% for the year ended December 31, 1998. The increase in international revenues was primarily attributable to the continued expansion of our European headquarters in Amsterdam, Netherlands, including an increase in sales personnel, and our acquisition of London-based Fletcher Research Limited on November 15, 1999. During 1999, we invoiced our international clients in US dollars, except for those billed by Fletcher Research Limited. Cost of Services and Fulfillment. Cost of services and fulfillment decreased as a percentage of total revenues to 32% in the year ended December 31, 1999 from 36% in the year ended December 31, 1998. These expenses increased 26% to $27.7 million in the year ended December 31, 1999 from $22.0 million in the year ended December 31, 1998. The decrease in expenses as a percentage of revenues reflected a larger revenue base in 1999 and lower production costs resulting from the introduction of our eResearch platform in March 1999. The expense increase in 1999 was principally due to an increase in research analyst staffing and related compensation expenses. Selling and Marketing. Selling and marketing expenses increased as a percentage of total revenues to 36% in the year ended December 31, 1999 from 34% in the year ended December 31, 1998. These expenses increased 49% to $31.1 million in the year ended December 31, 1999 from $20.9 million in the year ended December 31, 1998. The increase in expenses and expenses as a percentage of revenues were principally due to the increase in the number of direct sales personnel and related commission and travel expenses. General and Administrative. General and administrative expenses remained constant as a percentage of total revenues at 11% in the years ended December 31, 1999 and December 31, 1998. These expenses increased 48% to $9.9 million in the year ended December 31, 1999 from $6.7 million in the year ended December 31, 1998. The increase in expenses was principally due to staffing increases in our technology, operations, finance, and strategy groups. Depreciation and Amortization. Depreciation and amortization expenses increased 45% to $4.0 million in  the year ended December 31, 1999 from $2.8 million in the year ended December 31, 1998. The increase in these expenses was principally due to purchases of computer equipment, software, office furnishings, and leasehold improvements to support business growth, including our move to our new headquarters in October 1999.