Paid Search (SEA): What It Is, How the Auction Works, What It Costs and How It Compares to SEO

The French terminology commission defines paid search, as recorded in the Office québécois de la langue française terminology record (2022), as the set of techniques that give a website, for a fee, a better position in search engine results. This guide explains how the auction works, which formats exist in 2026 (including ads inside Google's AI-generated answers), what it costs, and when paid search beats SEO.

What is paid search?

Paid search covers the ads bought on search engines: Google Ads for Google, Microsoft Advertising for Bing and its partners. Ads appear above and below the organic results, as text or product listings, and in the vast majority of cases the advertiser pays per click.

Four terms come up constantly and overlap:

• Paid search (SEA): advertising on search engines.
• SEO: work on the site and its content to appear in the unpaid results.
• SEM (search engine marketing): SEO plus paid search, although many people use it as a synonym for paid search.
• PPC (pay per click): the billing model, also used outside search engines (social networks, partner sites).

Paid search runs on search intent: the ad shows at the exact moment people describe their need themselves ("emergency plumber chicago", "invoicing software"). That is what sets it apart from social media advertising, which targets profiles.

How does the paid search auction work?

On every search, Google runs an auction between the advertisers whose keywords match the query. Price is not the only criterion: according to Google Ads Help on Ad Rank, ranking takes into account your bid, the quality of your ad and landing page, Ad Rank thresholds, the competitiveness of the auction, the context of the search (location, device, time, search terms) and the expected impact of assets and other ad formats.

1. The search triggers the auction

The system keeps the ads whose keywords and targeting (location, language, audience) match the query.

2. A first Ad Rank calculation filters eligible ads

Google calculates Ad Rank once to decide whether the ad can show, then a second time to set its position against the other eligible ads. An ad below the threshold does not appear, whatever the bid.

3. Quality weighs as much as price

Google summarizes that quality for each keyword in the Quality Score (rated 1 to 10), which combines expected click-through rate, ad relevance and landing page experience. A highly relevant ad can win a better position than a competitor bidding more.

4. You pay the minimum required

The cost per click (CPC) actually charged is often lower than your maximum bid. Google states in its help page on actual CPC that you only pay what is minimally required to clear the Ad Rank thresholds and the advertiser ranked just below you. With automated bidding (maximize conversions, target CPA or target ROAS), Google's algorithm sets the bid for each query.

What are the paid search ad formats?

Text ads on the Search Network are still the core of paid search, but ad platforms offer other formats, increasingly bundled into automated campaigns. Our guide to how Google Ads works walks through the platform step by step.

For online stores, Google Shopping ads often take most of the budget. Bing works much like Google: our guide to Microsoft Advertising (Bing Ads) shows how to import an existing campaign.

Ads in AI Overviews are the most recent change. According to Google Ads Help on ads and AI Overviews (checked October 2026), text and Shopping ads from Search, Shopping and Performance Max campaigns can show inside the AI-generated summary, in English only and in 12 countries (including the US, Canada, India and Australia). Above and below AI Overviews, ads are eligible in 200+ markets. Sensitive verticals (healthcare, finance, gambling, alcohol, politics) are excluded, and advertisers can neither target nor opt out of the placement. Other assistants are opening up to advertising too: see our article on ads in ChatGPT.

How much does paid search cost?

There is no fixed price: you set a daily budget and a bidding strategy, and cost depends on competition for your keywords. Google does not publish average CPCs by country or industry; the best references are studies of large samples of campaigns.

The annual WordStream by LocaliQ study, reported by Search Engine Journal (June 2026), covers thousands of US Google Ads and Microsoft Ads campaigns between April 2025 and March 2026:

These averages describe the US market and hide wide gaps: legal and financial services pay far more per click than entertainment or retail. To estimate your budget, start from your goals: 1,000 clicks a month at $2 is $2,000; at a 3% conversion rate that gives 30 conversions, or about $67 per conversion. Our guide to Google Ads cost covers the levers that move these numbers.

SEO vs paid search: what are the differences?

Both target the same results pages but work in completely different ways. The table sums up the gaps that matter for a decision.

Marginal cost makes the difference over time: in paid search, doubling traffic doubles the bill; in SEO, a well-ranked page brings visits at no extra cost. The SEO vs paid search savings calculator estimates what the organic traffic you already get would cost you in ads.

When should you combine paid search and SEO?

Most businesses that invest in paid search gain from running SEO in parallel. Five situations make paid search especially worthwhile:

1. Launch of a site, product or offer: ads bring traffic while pages earn their organic positions.
2. Seasonality: sales, back to school, holidays, when you need visibility right away for a short period.
3. Keyword testing: a few weeks of ads reveal which queries convert, before you invest in SEO content on those topics.
4. Brand queries: when competitors bid on your name, an ad protects the top spot.
5. Highly commercial queries dominated by big sites, where a strong organic position takes years.

For informational queries ("how", "why", "what is"), SEO usually gives a better return, because those clicks convert poorly and are expensive to buy.

How do you measure a paid search campaign?

Without reliable conversion tracking, automated bidding optimizes blind. Set it up before launching any campaign, then track these metrics:

• Click-through rate (CTR): how relevant the ad is to the query.
• Average CPC: the price of attention on your keywords.
• Conversion rate: how well the landing page turns the click into an action.
• Cost per acquisition (CPA): spend divided by the number of conversions.
• ROAS: revenue generated divided by ad spend. The ROAS calculator gives your break-even point based on your margin.

Check the search terms report every week as well: it shows the real queries that triggered your ads and lets you add negative keywords.

Paid search, SEO and GEO: being visible in AI answers

A growing share of searches ends in a generated answer: Google AI Overviews, ChatGPT, Gemini or Perplexity. Paid search places ads around or inside that answer, but it does not buy a citation as a source. AI assistants cite pages they judge reliable and useful, and our study of the platforms AI assistants cite most shows those sources are mostly editorial content, forums and reference sites.

Getting recommended by AI therefore takes solid content on your customers' questions, plus monitoring of what assistants say about you. AI brand mention tracking shows which questions cite you and which competitor is cited instead.

Paid search buys immediate visibility; SEO and GEO build visibility that stays when the budget stops. To feed that second lever without spending your days on it, Sorank's article generator finds your keywords, then writes and publishes articles optimized for Google and AI on autopilot, with a 3-day free trial.