19 is maximum number of sixes hit in a one day innings, done by India vs Australia, followed by 18 by South Africa against Netherlands, India against Bermuda, New Zealand against Ireland and India against New Zealand. South Africans made 353 for 3 wkts in just 40 overs that day with 7 sixes from Herschelle Gibbs, 5 from Jacques Kallis, 4 from Mark Boucher and 2 from Graeme Smith. Poor Netherlands lost the match by wooping 221 runs.
On 19 March 2007, during world cup, Indians were defeated by Bangladesh and now needed to better their net runrate against Bermuda and win over Sri Lanka to qualify for super 8s and hence, all their batsmen chanced their arms over minnow team to post 413 for 5 wkts that day. Yuvraj Singh his 7 sixes, Sachin Tendulkar 4, Virendra Sehwag 3, Sourav Ganguly 2 while MS Dhoni and Rahul Dravid hit a six a piece. India won the match by 257 runs but lost to Sri Lanka to boo out of that Caribbean world cup.
18 sixes by New Zealand over another small team, Ireland, is interesting one as Brendon McCullum himself hit 10 of those, making 166 that day. his opening partner, James Marshall, made career best 161 with 4 sixes while other 4 big ones were smashed by Ross Taylor, New Zealand made 402 and won the game by, hold your breath, 290 runs!
India v New Zealand, 8 march 2009 : is one match I'll never forget. 31 sixes were hit that day, 18 by India and 13 by New Zealand as record of most sixes in an ODI was broken into pieces and win margin was marginal 58 runs in favour of India.
Most sixes by a team in a one day international
19 sixes = India vs Australia at Bengaluru, 21 fours, 2 Nov 2013.
18 sixes = South Africa vs Holland at Basseterre, 30 fours, 16 Mar 2007.
18 sixes = India vs Bermuda at Port of Spain, 30 fours, 19 March 2007.
18 sixes = New Zealand vs Ireland at Aberdeen, 28 fours, 1 July 2008.
18 sixes = India vs New Zealand at Christchurch, 32 fours, 8 March 2009.
16 sixes = New Zealand vs Zimbabwe at Bulawayo, 39 fours, 24 August 2005.
16 sixes = Australia vs New Zealand at Hamilton, 23 fours, 20 Feb 2007.
16 sixes = Pakistan vs Zimbabwe at Kingston, 27 fours, 21 March 2007.