Is the market for business travel by private jet looking healthy in the years ahead? NetJets, the private jet operator owned by Warren Buffet’s Berkshire Hathaway, is betting $9.6 billion that it is.

That’s the approximate dollar value of the massive new aircraft order that NetJets placed last week – said to be the largest such purchase in the history of private aviation. The company said it will add up to 425 planes to its worldwide fleet, with deliveries starting in 2014.

The order includes 100 firm orders and 175 options for Bombardier Challenger aircraft, in both the 300 and 605 series, with deliveries beginning in 2014. It also covers 25 firm orders and 125 options for Cessna Citation Latitudes, for delivery beginning in 2016.

NetJets’ newly announced shopping list is in addition to orders for up to 120 Bombardier Global aircraft that it placed in 2011 and up to 125 Embraer Phenom 300s ordered in 2010. The current NetJets fleet comprises 725 aircraft; some of the new ones will replace existing models in addition to allowing for growth of the business.

Besides its extensive U.S. operation, NetJets has a European division and a new joint venture operation in China. In 2010, it acquired Marquis Jet, a leading provider of jet cards, which entitle purchasers to a specified amount of flying time in private jets. The company claims to be the world’s largest provider of fractional ownership plans for private jets.

NetJets said the latest order, along with the 2011 and 2010 orders mentioned above, marks the launch of what it calls the NetJets Signature Series of aircraft. “The Signature Series planes are the first aircraft that NetJets helped design from start to finish,” a spokesman said. “These aircraft are bigger, faster, quieter and offer longer range than similar aircraft of the previous generation.”