A report released Monday by The Heritage Foundation said illegal immigrants create a deficit of $9.4 trillion over their lifetime because they receive much more in government benefits than they pay in taxes.
Using statistics from 2010, the organization said well-educated American citizens paid $29,250 more in taxes than they received in benefits.
The "typical" illegal immigrant has only a 10th-grade education, the report said, and are among poorly educated households that receive an average of $35,113 in benefits more than they pay in taxes.
The study rejected the belief that lawful immigrants use little welfare, saying they receive about the same or higher benefits than U.S.-born households with the same educational level.
While illegal immigrants don't currently have access to means-tested welfare, Social Security or Medicare, granting them amnesty would give them access to more than 80 means-tested welfare programs, the study said.
"Unlawful immigrants, on average, are always tax consumers; they never once generate a 'fiscal surplus' that can be used to pay for government benefits elsewhere in the society," the study contends. "This situation obviously will get much worse after amnesty."