Former students occupied an Oxford building on Monday to protest the university's failure to decide about divesting funds from fossil fuels.
Campaigners expected an announcement from the university, following discussion of a divestment proposal put forward by students.
But an Oxford spokesperson said time was needed to consider "serious issues" involved in the investment change.
The demonstrators said there was no excuse for delaying the decision.
They point out that firms have discovered three times more fossil fuel than can be safely burned without excessive risk to the climate.
A spokesperson for Oxford University said, "(The) Student Union raised an important and multi-faceted matter which requires thorough consideration."
Joining the occupation was John Clements, Oxford's director of finance from 1995 to 2004. He said: "We are bitterly disappointed about the university's failure to come to a decision. Oxford should be leading the move away from investment in all world-destroying fossil fuel companies to more sustainable forms of energy."
These events played out as the UN's climate body, the UNFCCC, said it supported divestment - and the Guardian newspaper launched a petition urging the Gates and Wellcome Trusts to divest.
Several top universities including Stanford and Glasgow have already decided to pull out of their shares in fossil fuels.
Oxford postponed its decision until May.
'Hear the voices'
The British Medical Association, the World Council of Churches and the Rockefeller Brothers have all agreed to divest and members of the London Assembly have urged the Mayor Boris Johnson to withdraw investments in coal, oil and gas.
This is said to be the fastest-growing divestment movement the world has seen.
Oxford is the second richest university in the UK after Cambridge. Its endowment is worth around £3.8bn. Over the last five years it has partially divested from arms manufacturing companies.
Two years ago the university accepted funds from Shell for a new Earth Sciences laboratory and the firm also funds research doctorates in geochemistry. BP spends millions supporting university research.
The Oxford Fossil Free campaign urges the university to evaluate the carbon risk of its portfolio; to move from high-carbon assets to low-carbon alternatives; and to cut direct investments in coal and tar sands oil - the most polluting energy sources.
It has gathered support from students, academics and alumni with over 100 academics signing an open letter calling for action.
Miriam Chapman, a student campaigner at Oxford University, said: "This decision could make climate history.
"Oxford University needs to hear the voices of its students, academics and alumni calling for action on climate change, and an end to investment in fossil fuels."
Globally, the organisers of the campaign claim that around 200 institutions with a combined asset size of over $50bn have committed to divest, although the small print of commitments leaves wriggle-room in some cases.
As the campaign grows, so does opposition to it. Daniel Fischel, emeritus professor at the University of Chicago Law School told BBC News: “Every bit of economic evidence suggests that fossil fuel divestment is a bad idea. The costs are substantial and stand to have real financial impacts on the returns generated by endowment funds.”
Jeremy Leggett, a solar entrepreneur and Oxford alumnus said: "I don't think universities should be training young people to craft a viable civilisation with one hand, and bankrolling its sabotage with the other."
Follow Roger on Twitter: @rharrabin