Proper motion and parallax for members, all identified O-type stars, and field stars in the search field centred on NGC 6618. The members and O-type stars are coloured and marked similarly as in Fig. 2. O-type stars with ruwe > 1.4 are not shown in both panels. Left: Proper motion distribution in the Galactic coordinate frame. We show for context the transverse velocity difference equal to ∼1 mas yr⁻¹ proper motion difference at the distance of NGC 6618 (1674 pc). The cluster proper motion determined with the mean of the members and from the runaways (see Sect. 4) are shown with the green and red cross respectively. Right: Parallax distribution as a function of the G-magnitude. The best-fit parallax and 1σ uncertainty of NGC 6618 determined from the members are shown with the grey dashed line and bar respectively.