The present disclosure generally relates to processes to produce alpha-olefin oligomers and poly alpha-olefins. In an embodiment, a process to produce a poly alpha-olefin (PAO) includes introducing a first alpha-olefin and a first catalyst system comprising a metallocene compound into a continuous stirred tank reactor or a continuous tubular reactor under first reactor conditions to form a first reactor effluent. The alpha-olefin is introduced to the reactor at a flow rate of about 100 g/hr or more. The first reactor effluent includes PAO dimer comprising at least 96 mol % of vinylidene and 4 mol % or less of trisubstituted vinylene and disubstituted vinylene, based on total moles of vinylidene, trisubstituted vinylene, and disubstituted vinylene. The method includes introducing the first reactor effluent, a second alpha-olefin and a second catalyst composition comprising an acid catalyst into a second reactor under second reactor conditions to form a second reactor effluent comprising PAO trimer.