AT A TIME of rising concern about big money donors to American universities, the elusive Bass brothers of Texas have emerged as one of the most generous and mysterious sources of funds.

Since 1990 the billionaire Bass oil family - patriarch Perry Bass, and sons Sid, Edward, Lee and Robert - have given $80 million to Yale, $25 million to Stanford and in their latest gift this month, $10 million to Duke University.

The most controversial to date has been Lee Bass's grant of $20 million to Yale, where he graduated in 1979. The money, earmarked for supporting courses in Western civilisation, was returned by university officials who said they could not honour Mr Bass's request to approve faculty appointments.

Donations to American universities by the South Korean and Turkish governments to establish courses and chairs in the studies of their regions have provoked charges that they are currying academic favour. The Bass family, by contrast, insist that their huge gifts come with no such strings attached. But the mystique surrounding this private dynasty has raised more than a few eyebrows.

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Edward Bass gave $20 million to Yale - also his alma mater - which established the Yale Institute of Biospheric Studies. He also gave millions of dollars to the Biosphere 2 project. That was the much ridiculed attempt to create a self-sustaining mini-world under a giant glass house in Arizona, though several Yale faculty members were involved and Columbia University has taken over its research programme.

The four brothers are credited with taking their father's oil fortune and multiplying it many times. They are known as aggressive investors in companies from Texaco to Walt Disney, where one brother was said to have engineered powerful Disney supremo Michael Eisner's rise to power. Recently they have been mired in controversy in California's Imperial Valley, where they bought 30,000 acres of farmland in what some describe as the latest episode in the fabled "water wars" of the American West. Local farmers have worried that the family are chiefly interested in selling water rights on the land to the southern California city of San Diego at a huge profit - a move, it is feared, that could literally suck the life out of local agriculture.

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Robert Bass, aged 48, an alumnus of Yale and Stanford business school, announced the $10 million gift to Duke with his wife Anne. Their son is an undergraduate there. Most of the money is in a challenge grant which Duke must match in order to collect. Thus it is soon to launch a $30 million fund-raising drive. Its goal is to improve campus teaching standards by endowing 25 chairs, with five-year terms, for professors "who have excelled in research and instruction", according to university president Nan Keohane.

Earlier this year Robert and Anne Bass gave $20 million to Yale - not long after Lee Bass had withdrawn his donation. That gift was expressly designed to renovate Yale's residential colleges, but was not a replacement for Lee's donation, a family spokesman said.

Their father, Perry Bass (Yale, 1937) gave $20 million in 1991 to celebrate his 50th wedding anniversary. Sid Bass, a 1965 graduate and the oldest brother, gave $20 million the previous year.