A few absorption lines of the (Q)Q branch of the a(1)Delta(g)-(0)-X(3)Sigma(g)(-) (1) hot band of pure O-2 have been detected near 1.58 mu m by CW-cavity ring down spectroscopy based on a fibred DFB laser. A sensitivity of the order of 2 x 10(-11) cm(-1) has been achieved by averaging a large number of spectra, allowing for the measurement of line intensities as weak as 5 x 10(-31) cm/molecule. The integrated band intensity is estimated to be S-01 = 4.5(7) x 10(-29) cm/molecule which differs by a factor of about 6 from the value provided by the HITRAN database. Our intensity value is supported by a significantly better agreement with the value deduced from the intensity of the a(1)Delta(g)(0)-X(3)Sigma g(-)(0) cold band and the respective Franck-Condon factors. (c) 2005 Elsevier B.V.. All rights reserved.