Teenagers who fall just short of their predicted A-level grades next week are set to face a scramble for the last remaining top university places.
Many leading universities have already declared they are full and will not be entering clearing this summer, while others expect to have just a handful of places available, according to a survey by the Press Association.
But changes to admissions means that students who get higher than predicted grades, and score at least two As and a B, may find they have more choice.
Under the new system, there is now no limit on the numbers of AAB students that universities can recruit, allowing them potentially to offer last-minute places to youngsters who do better than expected and meet this threshold.
It means universities are likely to have less flexibility to admit students who just miss this standard as there is still a strict cap on those who score less than AAB.
Students who score better grades than predicted, including those who unexpectedly gain AAB, can use the "adjustment" process to trade up to a different university.
Data gathered by the Press Association shows that a number of the leading Russell Group universities - considered among the best in the country - have no free places and will not be entering clearing again this year.
Clearing is the process that matches students who have not received offers, or who have been turned down by their original choices because they failed to meet the required grades, with available courses.
Oxford, Bristol, University College London (UCL), Cambridge, the London School of Economics and Political Science (LSE), Birmingham and King's College London will not be entering clearing again this year.
The figures suggests that the move to triple tuition fees to a maximum of £9,000 from this autumn will have an effect on clearing. Last year, some institutions saw a drop in available last-minute places because of a rise in applicants hoping to start university before the hike.