Technology and Finance were top categories for online advertising in 2004, according to AdZone.
| Rank | Category | Estimated Expenditures |
Impressions |
| 1 | Technology | $181,406,100 | 14,602,000,000 |
| 2 | Finance | $89,730,650 | 7,020,786,000 |
| 3 | Automotive | $64,027,400 | 6,975,806,000 |
| 4 | Retail | $61,747,100 | 5,688,070,000 |
| 5 | Business | $50,274,300 | 4,427,728,000 |
| 6 | Travel | $47,382,700 | 4,286,857,000 |
| 7 | Home | $33,821,500 | 1,923,517,000 |
| 8 | Entertainment | $32,463,700 | 2,258,371,000 |
| 9 | Sports & Leisure | $30,720,100 | 2,184,377,000 |
| 10 | Health | $28,052,400 | 2,775,364,000 |
| Source:AdZone | |||