  We present new time-series CCD photometry, in the B and V bands, for the
moderately metal-rich ([Fe/H] ~ -1.3) Galactic globular cluster (GC) M62 (NGC
6266). The present dataset is the largest obtained so far for this cluster, and
consists of 168 images per filter, obtained with the Warsaw 1.3m telescope at
the Las Campanas Observatory (LCO) and the 1.3m telescope of the Cerro Tololo
Inter-American Observatory (CTIO), in two separate runs over the time span of
three months. The procedure adopted to detect the variable stars was the
optimal image subtraction method (ISIS v2.2), as implemented by Alard. The
photometry was performed using both ISIS and DAOPHOT/ALLFRAME. We have
identified 245 variable stars in the cluster fields that have been analyzed so
far, of which 179 are new discoveries. Of these variables, 133 are fundamental
mode RR Lyrae stars (RRab), 76 are first overtone (RRc) pulsators, 4 are type
II Cepheids, 25 are long-period variables (LPV), 1 is an eclipsing binary, and
6 are not yet well classified. Such a large number of RR Lyrae stars places M62
among the top two most RR Lyrae-rich (in the sense of total number of RR Lyrae
stars present) GCs known in the Galaxy, second only to M3 (NGC 5272) with a
total of 230 known RR Lyrae stars. Since this study covers most but not all of
the cluster area, it is not unlikely that M62 is in fact the most RR Lyrae-rich
GC in the Galaxy. In like vein, we were also able to detect the largest sample
of LPV's known in a Galactic GC. We analyze a variety of Oosterhoff type
indicators for the cluster, and conclude that M62 is an Oosterhoff type I
system. This is in good agreement with the moderately high metallicity of the
cluster, in spite of its predominantly blue horizontal branch morphology --
which is more typical of Oosterhoff type II systems. We thus conclude that
metallicity plays a key role in defining Oosterhoff type. [abridged]
