Our deep survey in the COSMOS field is sensitive to CO fluctuations at redshifts 0.3 < z < 2 (see the figure below). While this is a foreground signal for [CII] (figure below, right), it is also a chance for investigating the star formation and gas content of galaxies at lower redshift, as CO is the most abundant molecular species (after H2) tracing the metal enriched, relatively dense, cool to warm molecular ISM phase where stars efficiently form. In particular, cross-power spectrum of two CO lines at the same redshift, within CONCERTO, can give a measure of the 3D clustering of undetected galaxies and the distribution of molecular gas in the cosmic web. We will obtain the relation between the CO luminosity and dark-matter halo mass and an other estimate of the SFRD and molecular gas density at z < 2.