2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/4278We show that it is impossible to determine the state equation of quintessence models on the basis of pure observational SNIa data. An independent estimate of $Ω_{M0}$ is necessary. Also in this most favourable case the situation can be problematic.7 pages, 4 figures - RUBANO@NA.INFN.ITAstrophysicstext