[11] Tickets for the festival were on offer as prizes to those who filled in an online survey won by Kings of Leon, the first headliner announced for the second consecutive year on 28 January 2009.

[22] Hot Press then announced what they claimed was a "world exclusive" late on 28 January 2009 that Snow Patrol and The Killers, headliners in 2007, would be co-headliners in 2009.

[27] On 5 February, the reformed Blur were announced as the remaining headliners in what was their only Irish appearance of the year[28][29] and their first in Ireland since three shows in the Olympia Theatre, Dublin in 2003.

[30][31] It will also be only the third time that all the original members will be together since 2000,[32] with the second occurring a week earlier in Hyde Park, London[33] at a 55,000 sell-out show[34] which followed an appearance at Glastonbury 2009.

[39][40][41] On 24 February, Keane, Lily Allen, The Specials, Paolo Nutini, Wallis Bird, Digitalism, The Mars Volta, Swedish House Mafia, Miss Kittin/The Hacker, Crookers, and Hockey were confirmed by MCD.

[42] The Specials were announced after they reformed to celebrate thirty years in the music business, although it was unclear at the time if founding member Jerry Dammers would be included.

[43] The Truffle Shuffles learned of their invitation to perform whilst live on Rick O'Shea's RTÉ 2fm radio show on 25 February.

These were Lady Gaga, Manic Street Preachers, Florence and the Machine, TV on the Radio, The Game, Ladyhawke, James, Foals, Of Montreal, Friendly Fires and Squeeze.

These included Nine Inch Nails, Jane's Addiction, Pet Shop Boys, Glasvegas, The Saturdays, Doves, Eagles of Death Metal and God Is an Astronaut.

[47][48][49] Techno/electronica musicians Niall "Mano le Tough" Mannion and Ruairi Donohue of the Red Bull Music Academy also performed at Oxegen in 2009.

[51] Calvin Harris, Noisettes, The Saw Doctors, The Coronas, The Blizzards, The Answer, The Horrors, Iglu & Hartly, Starsailor and Spinnerette were added to the line-up on 28 April.

[61][62] Also performing on that stage are C O D E S, Heathers, Blood or Whiskey, Juno Award winners Wintersleep, Broken Record from Scotland, Home Star Runner and Concerto For Constantine.

[68] The Irish Minister for Communications, Energy and Natural Resources Eamon Ryan endorsed a "Rock the Environment" competition designed to promote Oxegen 2009 as being a "green festival".

[69] Box Social, Colin Scallan, I Phoenix, The J-Walkers, The Resistance and Seven Days were the six finalists; two were selected in Naas, County Kildare on 19 June.

[73] It included the favourite Oxegen moments of six Irish musicians[74] and interviews with Brody Dalle of Spinnerette[75] and Dave Keuning of headliners The Killers.

[78] Lightbody also wrote a guide to surviving festivals, interviewed Glenn Moule of the band Howling Bells and wrote a piece on which artists he intended to see perform at Oxegen, including Lily Allen, Republic of Loose, Patrick Wolf, TV on the Radio, Annie Mac, Elbow, Friendly Fires and Crystal Castles.

[95] Dublin Bus, which operates public transport from Parnell Square to Punchestown, said its journeys were running at one hour and ten minutes, a "good" time according to the company.

[98] She had flown in from Belgrade and her performance included a cover version of "Womanizer" by Britney Spears and "Fuck You", her ode to George W. Bush, which had the crowd raising their middle fingers during the chorus.

[8][110] They played songs from three decades and paid tribute to an Irish music journalist who had assisted in their rise to fame, dedicating "There's No Other Way" to him,[15] with lead singer Damon Albarn saying: "The first time we were here [in Ireland] was back in 1990.

[108] Kings of Leon headlined Oxegen from 23:30 on the Saturday[110] despite threatening to withdraw from the festival after encountering serious sound problems at their T in the Park show in Scotland the day before.

[111] The sound problems frustrated vocalist Caleb Followill and led him to destroy his guitar before hurling the shattered remnants into the crowd.

[110] Lady Gaga underwent a wardrobe malfunction live on stage during her Sunday performance when one of her breasts slid from beneath her metallic dress.

[114] Sunday night headliners The Killers attracted large crowds to the main arena but attendance at Manic Street Preachers and Nine Inch Nails suffered from those bands performing at the same time on other stages.

[114] The first part of the line-up for the Hot Press signing tent was announced on 7 July 2009, with acts including Paolo Nutini, Razorlight, The Virgins, Fun Lovin' Criminals, The Blizzards, Hockey, Duke Special, Republic of Loose, The Coronas, Spinnerette, Friendly Fires and Therapy?.

[123] Duke Special was greeted by several males in superhero costumes,[122] whilst one fan who received an autograph from Brody Dalle of Spinnerette claimed she would have it tattooed onto her.

[131] Annoyed at this rejection, O'Driscoll left the festival early and flew to Dublin's RDS venue for a Bruce Springsteen concert, where he had a much more enjoyable time and cried when The Boss complimented him on stage on his sporting prowess.

[132] Pete Doherty, Kelly Jones and Natalie Portman, the latter of whom was seen buying pasta at one point,[112] also attended the Kings of Leon show at Oxegen 2009.

[139] In one serious incident, a man in his twenties was left in a stable condition after being stabbed with a glass bottle in a car park close to midnight on the Friday.

[100] Approximately 1,000 personnel and Scout volunteers were clearing the site of stage equipment, litter and abandoned tents by Monday afternoon.

[100] The Irish Independent reported that Punchestown Racecourse resembled "a scene from the World War I battle trenches" after being battered by heavy rain,[144] whilst the Irish Examiner suggested that the Ploughing Championships had arrived in Dublin the day after the festival so noticeable were the "wellie-wearing punters [who] stepped off buses, full of cheer, bearing muddy rain jackets and laden with picnic and camping equipment".