Admission tests are often used for medicine and law
One in seven universities is now using entrance tests as part of its selection procedures, a report says.
The Universities UK (UUK) report says 14% of higher education institutions now use one or more written tests.
Such tests are thought very useful for identifying very able applicants on high-demand courses but are not limited to these, the UUK report says.
But it warns that tests could place an extra financial burden on would-be students from poorer backgrounds.
Both Oxford and Cambridge universities use entrance tests for at least some subjects, and other universities use admission tests for students wanting to study medicine or law.
In June, Imperial College London said it would be introducing entrance tests for courses other than medicine because grade inflation had made it difficult to use A-level results to distinguish the best students.
The UUK report also suggests that increasing the number of tests used by universities could lead to "an undesirable (and profitable) industry that would provide coaching for those who could afford it".
Liberal Democrat universities and skills spokesman Stephen Williams said there was a risk that universities selecting by exam could act as a further barrier to widening participation.
"Taking such tests can be costly and pupils from better-off backgrounds are more likely to be 'coached' in advance.
"Ministers should at least give serious consideration to radically overhauling the admissions system so that students apply after they receive their A-level results.
"Bright pupils who have not considered applying to university may then rethink their decision once they have got their results.
"It would also give institutions more confidence in prospective students' abilities, rather than expecting them to rely on predicted grades," Mr Williams added.
However, the Universities UK report warned that there was not enough time between the publication of A-level results and the beginning of the university year in September and October for admissions to be decided and processed.
"The need for more time to complete a post-qualification admissions process than the summer period allows has led to suggestions that the start of the university year should be deferred to the following January."
This could affect candidates from backgrounds with little or no financial support in the intervening period and could lead to a loss of enthusiasm for higher education, it added.