Noble Energy’s high-quality portfolio is distinguished by its diversity, exploration component and sizeable international holdings. Each asset fills an important role in a portfolio that balances lower-risk development projects with high-potential exploration activities. With an asset mix that includes both United States and international opportunities in oil and natural gas, we have many options that allow us to employ our knowledge, replicate our successes and create value for many years to come.
Our onshore assets in the U.S. deliver steady, consistent and predictable results. We are targeting significant onshore growth over the next five years, led by liquid-rich and emerging resource opportunities. In early 2010, we enhanced our onshore position with a bolt-on acquisition to our significant DJ Basin assets. In the DJ Basin is our largest onshore property, the Wattenberg field, where we have a very successful legacy of resource development and are applying new technology to further enhance field recoveries. Noble Energy further enhanced its position in 2011 by acquiring Marcellus Shale properties in southwest Pennsylvania and northwest West Virginia. Driven by exploration, activities in the deepwater Gulf of Mexico focus on significant opportunities where projects can be a source of medium and long-term growth. With key positions offshore Equatorial Guinea and Israel, our international business provides long-lived production in basins with significant running-room.
Our exploration program has delivered a significant lineup of major development projects over the last few years, highlighted by the Leviathan success offshore Israel. It is the largest discovery in Noble Energy's history at 18 trillion cubic feet of gross natural gas mean resources. As we appraise and develop the substantial resources discovered, significant growth in proved reserves, production and cash flow will be realized well into the decade.
In addition, we have built a large inventory of further exploration upside that has the potential to deliver continued growth for our company. A number of significant opportunities build on our core operational areas where substantial success has already been achieved: onshore in the U.S., the deepwater Gulf of Mexico, offshore West Africa and offshore Eastern Mediterranean.