The Environmental Integrity Project, which describes itself as a nonprofit and nonpartisan group that wants to see better enforcement of environmental laws, said 20 sites did not disclose nearly 16,000 tons of pollutants they released in 2003.

They include 15 gas-processing plants, two refineries a chemical plant and a carbon black site, the EIP said.

According to nearly 800 notifications to the Texas Commission on Environmental Quality in 2003, the 20 plants released a combined total of 19,200 tons of pollutants in 2003 as a result of upsets, maintenance, and startup and shutdown activity. But when submitting their total annual inventory of emissions to the state for that same year, the facilities admitted releasing only 3,400 tons of pollution, the report states.