Amongst the different techniques applied up to now to the search for solar g--modes (peaks identification, study of the phase/power coherence, the P0 - nur diagrams, etc ldots), some ones are primarily based on the use of their asymptotic behaviour: the constant separation in period between consecutive modes of the same degree ell. The exact fractions technique is one of those and has already been applied to ground based helioseismology data (H.B. van der Raay, 1998). In the present work, the technique is fully tested in order to see of its adequacy when the asymptotic property is not fully accomplished, either because of the rotational splitting of the modes or because of the range of radial order values considered. The encouraging results obtained, led us to apply it to a temporal series of 690 consecutive days obtained with GOLF instrument on board SOHO. The results are shown by Gabriel et al. in this Workshop.