NEW YORK ( TheStreet) -- Chesapeake Energy ( CHK), Penn Virginia ( PVA), Carrizo Oil & Gas ( CRZO), Consol Energy ( CNX), Rex Energy ( REXX), Gastar Exploration ( GST), ECA Marcellus Trust ( ECT), The Williams ( WMB) and Magnum Hunter Resources ( MHR) are Marcellus stocks with analysts' buy ratings of 88%, as polled by Bloomberg. Based on average 12-month price targets, the above stocks have up to 41% upside potential.The Marcellus Shale is the largest natural gas shale play in the U.S. and the most attractive target for energy development. Although the formation was recognized as a reservoir rock for several decades, recent high oil prices and drilling technology upgrades rendered the asset economically viable. The development of Marcellus region between Pennsylvania and West Virginia is under way. Engelder, a geosciences professor at Pennsylvania State University estimates recoverable natural gas reserves in the region at 489 trillion cubic feet (Tcf). The Marcellus is estimated to be the second largest, behind the South Pars field in Qatar and Iran, and the value of recoverable reserves is pegged at around two trillion dollars. Economic and environmental benefits of natural gas would ensure the development of the Marcellus basin. From about 1,100 wells drilled in West Virginia and Pennsylvania during 2010, the well count is expected to increase to 1,700 by 2020. Given this scenario, Marcellus natural gas production could reach 4 billion cubic feet per day by 2020 compared to 600 million cubic feet during 2009. Besides employment, development of the Marcellus Shale will improve tax collections to local, state and federal governments to around $9 billion by 2020 from $1.7 billion in 2009. Key factors that could hamper the development of the Marcellus basin are stringent environmental regulations and imposition of severance tax that could challenge future activity in this region. We have identified 9 Marcellus Shale stocks that received analysts' top buy ratings and hold the potential to deliver attractive returns over the next one year. Analysts' consensus estimate indicates an average return of 16% for the portfolio and the potential to deliver up to 40% upside over the next one year.