The Inventory Owns Your Media Plan.

By early 2026, principal media is predicted to account for nearly a third of all agency billings. That conflict doesn't sit in a footnote. It sits in your media plan.

There is a version of a media planning conversation where the agency recommends the channels that are best for your business. Then there is the version that is increasingly common: the agency recommends the channels where it already owns the inventory.

Those are different conversations and these days most advertisers can't tell which one they're in.

What principal media actually means

Principal media is when an agency (typically a holding company) pre-buys media inventory in bulk from publishers or platforms and then resells it to clients at a markup it doesn't disclose. The agency is not acting as your agent. It is acting as a vendor with a position to clear. It takes the margin on the spread, not a fee for the advice.

This is not a niche practice. According to Digiday's reporting on principal media, by early 2026 principal media is predicted to account for nearly 33% of total agency billings, driven by brands seeking perceived cost efficiency in a volatile market. The markup on that resold inventory can be significant, according to Marketing Procurement iQ's analysis of proprietary media. Agencies are typically not required to disclose it.

The disclosure problem really is a structural one. An agency operating on a fee-for-advice model has one interest: recommend what works. An agency with pre-bought inventory has a second interest: move the position. When those two interests conflict, the advertiser usually loses, and usually doesn't know it happened.

Why the brand-to-performance balance is the first casualty

The conflict doesn't play out evenly across a media plan. It concentrates in the channels and formats where principal inventory is easiest to hold: premium video, programmatic display, digital out-of-home, connected TV. These are not inherently bad channels. The problem is when the recommendation to use them is driven by what the agency needs to offload rather than what the plan needs to do.

For brands running integrated media, the damage tends to show up in the brand-to-performance balance first. Upper-funnel brand investment is discretionary in a way that paid search is not. A holding company sitting on a block of premium video inventory has an obvious incentive to frame that inventory as brand-building necessity. This planning bias also shuts out smaller, more innovative media partners who don't participate in bulk deals at all.

A fee-based independent has none of these incentives. It can tell you when brand investment is right and when it isn't, because it doesn't have a position that benefits from the answer going one way. We have seen this play out across clients who come to us after years inside holding-company relationships. The media mix reflects what was available, not what was optimal. Unwinding it takes time.

Independence is a structural protection, not a preference

The argument for working with an independent, fee-based agency is often framed as a values question: transparency is good, opacity is bad. That framing is true but undersells the point.

Independence is a structural protection. When the agency has no inventory to move and no rebate to collect, the only thing it can sell is the quality of its advice. That alignment is not a nice-to-have. It is the mechanism that keeps your media plan pointed at your business goals instead of someone else's balance sheet.

Other.™ is flat-fee based, with a percentage of our fees typically locked up in hitting our clients' business objectives. We take no commissions, no rebates, and no principal positions. We have no inventory to clear. Every recommendation we make is exposed to the same question: does this serve the client's outcome? That's the only question we're answering.

At nearly 33% of billings, principal media is not a niche risk. It is a structural feature of how most large agency relationships now work. The question worth asking before your next planning cycle is not whether your agency is transparent. It's whether the structure of your relationship makes transparency possible.

The bottom line: when an agency holds the inventory, the inventory holds the plan.

If you're evaluating your agency relationship ahead of next quarters planning, we're here to help.

Sources: Digiday, Rising demand for principal media buying underpins WPP's turnaround plan; Marketing Procurement iQ, The rise of Proprietary Media: how procurement should respond.