are within the scope and spirit of the invention accordingly the exemplary embodiments of the invention described herein and provided in the appended figures are set forth without any loss of generality and without imposing limitations relating to the claimed invention in one aspect the present invention is directed carbon based fluorescent nanoparticle tracers hereinafter referred to as u201c a dots u201d and u201c a nps u201d as either stand alone particles or building blocks for use in analyzing petroleum reservoirs the nanoparticle tracers have sufficient long term stability in both high temperature and high salinity environments allowing the tracers to survive transit through the subsurface between wells the nanoparticle tracers can be introduced into the reservoir through an injector well where they flow through the reservoir they can be detected sampled examined and tested reliably when the nanoparticles are recovered back at the surface from a producer well in certain embodiments the nanoparticles can include nanosized fullerene or carbon nanotubes in alternate embodiments the nanoparticles are not fullerene or carbon nanotube materials in certain embodiments the nanoparticles can include materials having a strong fluorescence signature in certain embodiments the nanoparticle tracers are stable at temperatures up to about 100 u00b0 c or greater alternatively 200 u00b0 c or greater and at salinity concentrations of about 75 000 ppm alternatively about 120 000 ppm or greater in the presence of monovalent.