The circular rotation speed of the Milky Way at the solar radius , \Theta _ { 0 } , has been estimated to be 220 km s ^ { -1 } by fitting the maximum velocity of H I emission as a function of Galactic longitude .
This result is in tension with a recent estimate of { \Theta _ { 0 } } = 240 km s ^ { -1 } , based on VLBI parallaxes and proper motions from the BeSSeL and VERA surveys for large numbers of high-mass star forming regions across the Milky Way .
We find that the rotation curve best fitted to the VLBI data is slightly curved , and that this curvature results in a biased estimate of \Theta _ { 0 } from the H I data when a flat rotation curve is assumed .
This relieves the tension between the methods and favors { \Theta _ { 0 } } = 240 km s ^ { -1 } .