The structure of traditional, linear phenol-formaldehyde (PF) resins and phenol-furfural (P-Furan) resins has been investigated by matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectroscopy.  The structure of a variety of oligomers has been obtained and the structures present in each of the two types of resins related to the reagent used either formaldehyde or furfural.  The oligomers type and species distribution appeared rather different for each case. Comparison of a P-Furan resin with a Mimosa tannin-Furan resin showed some differences. This latter shows a greater proportion of self-condensed fuanic oligomers due to the manner in which it is prepared starting from furfuryl alcohol. Several different Tannin-Furan oligomers were also observed by MALDI TOF analysis.