The 28 watercolours, supposedly painted at the beginning of her career during the First World War, are close to a major theme of her work - vivid, semi-abstract depictions of the Texan desert. Known as the Canyon Suite, they were purchased for $5.5m (pounds 3.4m) by R Crosby Kemper, a Kansas City banker, and put on show in his gallery, the Kemper Museum of Contemporary Art.
However, researchers compiling a full catalogue of O'Keeffe's work on behalf of the National Gallery of Art in Washington and the Georgia O'Keeffe Foundation of Abiquiu, New Mexico, say they have doubts about both the paper used and the painting style itself.
The director of the Kemper Museum, Dan Keegan, said he was conducting his own investigation and had already determined that not all the paintings date from between 1916 and 18 as thought.
At that time, O'Keeffe was living in western Texas and spent much of her time establishing what was to become her trademark style - the production of starkly modern works heavily influenced by the American southwest. It was a collection of these paintings that formed the basis of O'Keeffe's first public exhibition, in New York in 1917. The painter went on to a glittering career, dying in New Mexico in 1986 at the age of 99.
The Canyon Suite had previously withstood scrutiny by two researchers, Barbara Buhler Lynes, who is working on the catalogue, and Judith Walsh, senior paper conservator at the National Gallery.
Mr Kemper, who acquired the paintings in 1993 from Gerald Peters, an art dealer with galleries in New York and Santa Fe, believes the works may have been excluded from the catalogue out of spite because he did not donate them to the National Gallery. This is a charge the gallery denies.
Mr Peters has offered to buy back the works, now tentatively valued at around $8m (pounds 4.9m). If they turn out to be fakes, however, they will be deemed virtually worthless.