  The existence of long lived superheavy nuclei (SHN) is controlled mainly by
spontaneous fission and $\alpha$-decay processes. According to microscopic
nuclear theory, spherical shell effects at Z=114, 120, 126 and N=184 provide
the extra stability to such SHN to have long enough lifetime to be observed. To
investigate whether the so-called "stability island" could really exist around
the above Z, N values, the $\alpha$-decay half lives along with the spontaneous
fission and $\beta$-decay half lives of such nuclei are studied. The
$\alpha$-decay half lives of SHN with Z=102-120 are calculated in a quantum
tunneling model with DDM3Y effective nuclear interaction using $Q_\alpha$
values from three different mass formulae prescribed by Koura, Uno, Tachibana,
Yamada (KUTY), Myers, Swiatecki (MS) and Muntian, Hofmann, Patyk, Sobiczewski
(MMM). Calculation of spontaneous fission (SF) half lives for the same SHN are
carried out using a phenomenological formula and compared with SF half lives
predicted by Smolanczuk {\it et al}. Possible source of discrepancy between the
calculated $\alpha$-decay half lives of some nuclei and the experimental data
of GSI, JINR-FLNR, RIKEN are discussed. In the region of Z=106-108 with N$\sim$
160-164, the $\beta$-stable SHN $^{268}_{106}Sg_{162}$ is predicted to have
highest $\alpha$-decay half life ($T_\alpha \sim 3.2hrs$) using $Q_\alpha$
value from MMM. Interestingly, it is much greater than the recently measured
$T_\alpha$ ($\sim 22s$) of deformed doubly magic $^{270}_{108}Hs_{162}$
nucleus. A few fission-survived long-lived SHN which are either $\beta$-stable
or having large $\beta$-decay half lives are predicted to exist near
$^{294}110_{184}$, $^{293}110_{183}$, $^{296}112_{184}$ and $^{298}114_{184}$.
These nuclei might decay predominantly through $\alpha$-particle emission.
