FedEx ( FDX) has been benefitting from increased worldwide shipping volumes in 2012, buoyed by its enormous shipping network and the relative duopoly that the firm enjoys with top rival UPS ( UPS). Even though the two package delivery firms get compared with one another frequently, they're actually quite different. Unlike UPS, which integrates all of its shipping methods, FedEx has separate units for express shipments, ground shipments, and other modes of transport (such as freight and custom critical). That separation has made FedEx's operations stand out in recent years, and not in a good way. That's because the firm's dominant express unit was getting squeezed on margins at the same time UPS was churning out stellar performance from its league-leading ground operations. But now that FedEx Ground is delivering double-digits margins, things have changed enough that investors are willing to give the company the benefit of the doubt when it comes to financial performance. >>5 Stocks With Double-Digit Yields Barriers to entry are exceptionally high in the package shipping business, something that DHL learned when it unsuccessfully tied to become a player in U.S. domestic shipping. That should keep FedEx's place cemented as one of the critical shipping networks in the U.S. More near-term, lower fuel prices should help boost margins for the firm's massive truck and aircraft fleets.