Electron densities in laser-produced plasmas have been deduced from space-resolved spectra of oxygen-like ions Ca XIII, Ti XV, Fe XIX, Ni XXI and Cu XXII in the XUV (80-170 AA). The transition 2p6 1S0 to 2s2p5 1P1 has been identified for Cu XXII, the wavelength of the same transition for Ni XXI has been defined more precisely. Plasma images in the light of the different spectral lines have yielded the dimensions of the spatial regions in which Ca XIII, Fe XIX and Ni XXI exist.