 Osborne was well known for buying large libraries and offering the books for sale at fixed prices listed in catalogues.Most famously, after Edward Harley's death in 1741, Osborne purchased for £13,000 the extensive collection that had been assembled by Harley and his father, Robert Harley, 1st Earl of Oxford (Harley's collection of manuscripts was purchased by the British government and remains in the British Library as the Harleian Collection).Osborne hired William Oldys, who had been Edward Harley's literary secretary, and Samuel Johnson to compile a catalogue of the collection, which eventually ran to five volumes published from November 1742 to April 1745 under the name "Catalogus Bibliothecae Harleianae".