It's not as though Keith Urban and Carrie Underwood have any problems selling tickets to their individual concerts, but additional level of excitement and anticipation began building ever since their co-headlining tour was announced late last year. The two acts have been exceeding expectations from the time the tour launched in January.

In addition to their shows together, Underwood is continuing to headline her own North American tour with Josh Turner, and Urban is now in the process of finishing up an Australian tour that ends Saturday (March 29) in Sydney. Underwood and Urban will reunite on April 9 in Baltimore, but CMT Insider caught up with them earlier this month in Denver to talk about their Love, Pain & the Whole Crazy Carnival Ride tour.

"The whole tour in general, for me, has certainly been the most fun I've ever had on the road," Urban said. "The crowd interaction has been overwhelming, and I think next time we tour we're going to try and make that even more interactive because getting in there and being a part of everybody -- and playing with them instead of playing at them -- is really key, I think."

With any major concert production, keeping the performances fresh is a continuing challenge.

"We certainly try to keep as much spontaneity as we can," Urban said. "I mean, it's hard because it's not like playing in a club where you can just wing it on every song. There are lighting cues, and there's all sorts of things that people are relying on me to do so they know how to do their job. But, yeah, we throw in as much spontaneity as we can in the show."

Part of the spontaneity comes from the audience, especially when they participate in the performance.

"Every night we're learning something different," Urban noted. "People like to sing along with every song -- which is fantastic. It's amazing to hear that every night."

During the tour, Underwood has been getting a particularly strong response to her latest No. 1 single.

"There's a lot more fans singing along to 'All-American Girl,'" she said. "It's just because they've heard it more often on the radio. In the beginning, it was just my superfans singing along in the audience. Now, there's a lot more fans that, as soon as we start the song, recognize it and start cheering. So it's exciting to be able to sing one more song that everybody's heard at some point."

Underwood embraced the opportunity to tour with Urban.

"This is my first co-headlining situation, so I didn't really know what to expect going into it," she said. "It was just really fun to put together more staging, more lights, more songs and stuff like that. I have two albums now to sing off of -- which is great. The fans have been great. We've been selling out every single night, so it's just been wonderful."

Underwood and Urban have performed onstage together, but there hasn't been time for them to collaborate on any new music.

"Being out on the road, there's so much stuff going on that it's pretty much impossible to sit down for any length of time and write," she said. "I think it would be really hard for me and Keith to get together unless it was like after a show -- which would be like midnight -- to write a song. And by that time, we're usually heading on to the next place, so it's really a difficult time to do any collaborating with anybody. So we haven't worked on anything, but you never know."

CMT producer Dan Clark conducted the interviews for this story.