  Our long term aim is to derive model-independent stellar masses and distances
for long period massive binaries by combining apparent astrometric orbit with
double-lined radial velocity amplitudes (SB2). We follow-up ten O+O binaries
with AMBER, PIONIER and GRAVITY at the VLTI. Here, we report about 130
astrometric observations over the last 7 years. We combine this dataset with
distance estimates to compute the total mass of the systems. We also compute
preliminary individual component masses for the five systems with available SB2
radial velocities. Nine over the ten binaries have their three dimensional
orbit well constrained. Four of them are known colliding wind, non-thermal
radio emitters, and thus constitute valuable targets for future high angular
resolution radio imaging. Two binaries break the correlation between period and
eccentricity tentatively observed in previous studies. It suggests either that
massive star formation produce a wide range of systems, or that several binary
formation mechanisms are at play. Finally, we found that the use of existing
SB2 radial velocity amplitudes can lead to unrealistic masses and distances. If
not understood, the biases in radial velocity amplitudes will represent an
intrinsic limitation for estimating dynamical masses from SB2+interferometry or
SB2+Gaia. Nevertheless, our results can be combined with future Gaia astrometry
to measure the dynamical masses and distances of the individual components with
an accuracy of 5 to 15\%, completely independently of the radial velocities.
