On spindle type cotton harvesters, spindles are attached to bars which are arranged on rotating drums. Opposed drum harvesting units position one drum on each side of the row, whereas harvesting units with an in-line drum arrangement position both drums on the right side of the plant row. Two studies conducted in Australia and the United States focused on comparing drum arrangements in regard to harvesting efficiency and fiber quality as there has been no recent published research using high yielding commercial varieties. These studies concluded that there were slight, but insignificant differences among opposed and in-line drum arrangements in terms of harvesting efficiency and lint turn out. Although only statistically significant for the work conducted in the US, lint ginned from seed cotton harvested by the opposed drum arrangement contained more trash than that harvested by the in-line arrangement. In both countries there were small insignificant differences in terms of fiber color (both Rd and +b), length, and micronaire, after ginning and lint cleaning. Although not observed in Australia, small significant differences in length uniformity and strength were observed in favor of the opposed drum arrangement in the US. Measured only in Australia, there were no significant differences between the two drum arrangements in terms of short fiber index, fineness, and maturity. There was also no significant difference between the two drum arrangements in terms of total, fibrous and seed-coat nep content, and size.