They're questions which puzzle many music fans. Why do bands end up playing one festival and not another? Why do major talents end up lower on the bill than lesser ones? Jim Carrollpresents a rough guide to how acts get booked for festivals

I thought my favourite band were going to play Electric Picnic, but they ended up at Oxegen instead. I'm fuming. What gives?There are several reasons why bands end up playing one festival rather than another. It has a lot to do with a band's schedule, but most of these decisions come down to cash and - perhaps the most important person in the whole live-music equation - the agent.

I didn't know that Ari Gold from Entourage booked out indie bands.Ari probably has his hands too full with Vincent Chase at the moment to take on a couple of indie landfill acts. However, the vast majority of bands have an agent who book their tours, negotiate their fees and deal with the promoters.

When the bands make cash, they makes cash. The agent is the band's Ten-To-Fifteen Per Cent guy, and they are the ones with the real power.

This has to do with the whole live-music- is-the-new-rock-and-roll thing, right? Well, agents have always had a big say when it comes to who plays where and when. For the promoter putting on a show or festival, developing and maintaining a good working relationship with agents is essential.

I assume, then, that the agents play each promoter off against one other in the best interests of the band.In theory, yes. A band will decide they're going on the road and there's an opportunity for a few shows in Ireland.

The agent will then talk to the "big three" promoters (MCD, Aiken Promotions and POD) and, depending on the band, may also contact a few of the indie promoters such as Forever Presents, Umack and Foggy Notions. Like we said, that's what should happen.

I spot a "but" coming down the line.In reality, many agents prefer to deal with one of the "big three" for nearly all their acts. They have a relationship with an individual promoter so they will channel all their gigs through that promoter. Often, they will seek bids from other promoters (if the mooted venue is already booked, for example, or the dates don't suit) or give one of their newer acts to a different promoter, but usually they stick with who they know.

Of course, there are times when cash plays a part. An agent is not going to say "no" to a fee far in excess of what the band usually gets. Acts who may be with one promoter for indoor shows will and do play festivals for a different promoter, but this usually only happens after a huge fee is paid for the band's services.

Surely the act has a say in all of this?To be honest, the band usually goes along with their agent. After all, they're looking at the bigger picture and the agent is the go-to guy when it comes to big pay-days. Bands don't tend to argue with large wads of cash coming their way for a 45- to 60-minute set. They may have heard that Electric Picnic is a great festival, but the size of the fee for playing Oxegen trumps that. To bands, one festival is the same as the next. You arrive on site in your tour bus, have your dinner in the catering tent, play your gig and leave town right away.

This relationship between the agents and the "big three" must make it difficult for new and emerging festivals to book acts.True. Agents for high-profile acts prefer to deal with a small number of Irish promoters; they're unlikely to consider offers from new festivals and indie promoters. The latter complain time and time again about this, and it is why their festivals either feature rising independent acts or veteran bands who are happy to play anywhere that will have them.

The indie promoters may have €1 million to spend on the likes of The Eagles, but getting the band and their people to say yes is another story.

So if a band are initially booked by one promoter when they're starting out, they'll most likely stick with that promoter when they're selling out Croke Park? There are plenty of examples of such loyalty. REM's first Irish show in Dublin's SFX in 1984, for instance, was an MCD promotion and they've stayed with the company ever since. Likewise, Bruce Springsteen has always worked with Aiken when it comes to his blockbuster Irish shows.

But there are acts who do go around the houses for sport and increased fees.

Crystal Castles, for example, will have made three visits to Ireland this year by the end of 2008. Their Dublin show in April was with indie promoter Forever Presents; they're playing at Electric Picnic, which is a POD/Aiken co-promotion; and they're coming back for shows in October, promoted by MCD. At least they'll be able to compare how Irish promoters work when it's all over.

Getting back to festivals, I'm very curious about how bands end up where they do on the bill. Who decides this? The agent?A lot of it really comes down to common sense. Some bands are simply more popular than others and it would be rather silly for the festival organiser to have them lower on the bill or on a stage other than the main stage at the festival.

For example, you wouldn't have expected to see Rage Against The Machine anywhere other than top of the bill on the biggest stage at Oxegen.

As most bands spend the entire summer on the festival circuit, they soon learn their place in the greater scheme of things. They probably know without even looking who will be on before and after they take to the stage.

And the agent does play a role. They're usually there to ensure their act get their proper dues - but, sometimes, the agent will insist that his or her charges get a higher slot on the bill than to sooth troubled egos or make a point.

But there must be times when this placement goes awry?Yep, it happens. Back in 2006, NME's annual awards tour was headlined by Maximo Park, with Arctic Monkeys second on the bill. But between the time the dates were announced and the tour began, the Monkeys went supernova and I Bet You Look Good On The Dancefloor went to number one in the charts.

The vast majority of people, then, were there to see the Monkeys, but they were second on the bill - meaning many people had left for the nearest pub by the time headliners Maximo Park came onstage.

So we're unlikely to see any "surprise" headliners when the final line-up is released for the Electric Picnic?I think it's safe to assume that you will see the most promenient acts on the line-up ­ such as My Bloody Valentine, Sex Pistols and Sigur Ros at the top of the line-ups for the bigger stages. Anything else would be a bit of a surprise for fans (and probably the bands too).