Dr Brown attended the conference in the west African nation, Senegal, for a congress of global greens parties and organisations between March 27 and April 1 as a keynote speaker, at a cost to taxpayers of $19,967.

He announced his retirement from the Senate about two weeks later and formally quit on June 30.

Fellow Greens Senator Rachel Siewart, of Western Australia, attended the same conference, at a cost of $8173.

Details of Dr Brown's  trip to Senegal were contained in the latest Department of Finance and Deregulation statistics on the costs of federal MPs for January to June last year.

The details show that Senate Deputy President and Liberal Senator Stephen Parry outspent all his federal colleagues from Tasmania on domestic travel, costing $63,474 in flights and travel allowance.

Opposition leader in the Senate and Liberal Senator Eric Abetz came next with $55,716 in flights and travel allowance.

Denison independent MHR Andrew Wilkie ran up $41,315.

The low spenders included Labor Senator Carol Brown with $14,598 in flights and allowances, and Bass Labor MHR Geoff Lyons on $17,882.

In other details:

 Mr Wilkie spent $96,705 on office fitout costs at his Hobart office on the corner of Harrington and Collins Street, Mr Lyons spent $38,950, Braddon Labor MHR Sid Sidebottom spent $42,846 and new Labor Senator Lisa Singh spent $39,095.

 Other overseas travellers included Lyons Labor MHR Dick Adams, who spent $27,401 on a parliamentary delegation to Uganda and Kazakhstan, and Labor Senator Catrina Bilyk who spent $11,687 on a parliamentary delegation.

 Despite official moves to wind it back, the Life Gold Pass to free business class travel survives, with $533,709 claimed in the six months to last June from retired MPs and their families. The retired Tasmanian users included Max Burr, Paul Calvert, John Coates, Bruce Goodluck, Duncan Kerr, Jocelyn Newman, Peter Rae, Michael Tate, Michael Townley and John Watson. Users of a special travel entitlement for former MPs included Guy Barnett and Kerry O'Brien.