He left for the Californian goldfields in 1849 and returned in 1851, the venture being quite profitable for him. He entered business with much energy and a strong drive which along with sound commercial instincts allowed him to retire a very wealthy man in 1877. Another myth is that O'Neill purchased the Vineyard estate as a speculator in order to quickly sell it and make a healthy profit. The facts don't tend to support this view. After the purchase, he established his "Fairmount Estate" which covered a considerable portion of Rydalmere, the boundaries more or less extending from Park Road (formerly Wharf St) to Spurway Street, the southern boundary being the Parramatta river, and the northern boundary being Subiaco Creek (formerly Bishop’s Creek). It was an orchard and pasture property.