\documentclass[12pt]{article}

\usepackage{graphicx}

\textwidth   5.5in
\textheight  9.0in

\topmargin     0in
\oddsidemargin 0in

\begin{document}

\begin{figure}
\begin{center}
\includegraphics[width=0.8\textwidth]{opre_gbm1.eps}
\end{center}
\vspace{0.15in}
\caption{European call based on geometric Brownian motion}
\end{figure}

\begin{figure}
\begin{center}
\includegraphics[width=0.8\textwidth]{opre_gbm2.eps}
\end{center}
\vspace{0.15in}
\caption{Asian call based on geometric Brownian motion}
\end{figure}

\begin{figure}
\begin{center}
\includegraphics[width=0.8\textwidth]{opre_gbm3.eps}
\end{center}
\vspace{0.15in}
\caption{Lookback call based on geometric Brownian motion}
\end{figure}

\begin{figure}
\begin{center}
\includegraphics[width=0.8\textwidth]{opre_gbm4.eps}
\end{center}
\vspace{0.15in}
\caption{Digital call based on geometric Brownian motion}
\end{figure}

\begin{figure}
\begin{center}
\includegraphics[width=0.8\textwidth]{opre_heston.eps}
\end{center}
\vspace{0.15in}
\caption{European call based on Heston model}
\end{figure}

\end{document}