  We present a study of the X-ray properties of a volume-limited sample of
optically selected emission-line galaxies. The sample is derived from a
correlation between the KPNO International Spectroscopic Survey (KISS), an
H-alpha-selected objective-prism survey of AGNs and starbursting galaxies, and
the ROSAT All-Sky Survey (RASS). After elimination of all spurious matches, we
identify 18 ROSAT-detected X-ray sources within the KISS sample in the 0.1-2.4
keV band. Due to soft X-ray selection effects, the majority of the ROSAT
sources are Seyfert 1 galaxies. The majority (54%) of the ROSAT-KISS Seyferts
are classified as narrow-line Seyfert 1 objects, a relatively high percentage
compared to previous objective-prism-selected Seyfert galaxy samples. We
estimate the X-ray luminosities of the ROSAT-detected KISS objects and derive
volume emissivities of 6.63 x 10^38 ergs/s/Mpc^3 and 1.45 x 10^38 ergs/s/Mpc^3
for the 30 deg and 43 deg survey strips, respectively. For those KISS AGNs not
detected by RASS, we use the median L_X/L_H-alpha ratio derived from a previous
study to estimate L_X. The total 0.5-2 keV volume emissivity we predict for the
overall KISS AGN sample is sufficient to account for 22.1 +/- 8.9% of the soft
X-ray background (XRB), averaged over both survey strips. The KISS AGN sample
is made up predominantly of intermediate-luminosity Seyfert 2's and LINERs,
which tend to be weak soft X-ray sources. They may, however, represent a much
more significant contribution to the hard XRB.
