Mainline Investment Advisers provides portfolio management for individuals and small businesses and portfolio management for pooled vehicles. The firm advises 8 private funds.
Mainline Investment Advisers reports 16 clients. They include 9 pooled investment vehicles and 7 high-net-worth individuals. Of its assets, 76.8% ($84.4M across 6 accounts) are managed with discretion; $25.5M across 9 accounts are not. It advised 1 client without assets under management last fiscal year.
| Client type | Clients | Assets |
|---|---|---|
| High-net-worth individuals | 44% | 2% |
| Pooled investment vehicles | 56% | 98% |
Client breakdown and activity details
| Client type | Clients | Regulatory AUM | AUM share | Avg. per client |
|---|---|---|---|---|
| High-net-worth individuals | 7 | $2M | 1.8% | $286K |
| Pooled investment vehicles | 9 | $108M | 98.2% | $12M |
| Total | 16 | $110M | 100% | $6.87M |
- Clients
- 7
- Regulatory AUM
- $2M
- AUM share
- 1.8%
- Avg. per client
- $286K
- Clients
- 9
- Regulatory AUM
- $108M
- AUM share
- 98.2%
- Avg. per client
- $12M
Total
- Clients
- 16
- Regulatory AUM
- $110M
- AUM share
- 100%
- Avg. per client
- $6.87M
- Clients outside the U.S.
- 0%
- Clients advised without assets under management last fiscal year
- 1
- Private funds advised
- 8
Mainline Investment Advisers is paid through a percentage of assets under management, fixed fees (other than subscription fees), performance-based fees and other compensation; its fees and minimums are set out in its brochures on the SEC website.
Mainline Investment Partners, LLC owns 75% or more of Mainline Investment Advisers and is in turn owned by William Landman (50–75%) and David Clapper (25–50%). William Landman is CEO; the leadership team includes President David Clapper and Chief Compliance Officer Donna Rittershausen. It has 4 employees, 3 of them in advisory roles.
Leadership
- William LandmanPresident, Chief Executive Officer
- David ClapperVice President, Secretary, Chief Operations Officer
- Donna RittershausenChief Compliance Officer
Investment adviser representatives
2 representatives listed in the SEC register as of 9 October 2026.
- David Andrew Clapper
- William Alan Landman
Staff
- 4 employees
- 3 in advisory functions
- 2 state-registered reps
- 1 broker-dealer rep
- 1 insurance agent
- Owns 75% or more of Mainline Investment Advisers, LLC
Mainline Investment Partners, LLC
Control person · since August 2011
- Owns 50% to 75% of Mainline Investment Partners, LLC
William Landman
Control person · since August 2011
- Owns 25% to 50% of Mainline Investment Partners, LLC
David Clapper
Control person · since August 2011
Mainline Investment Advisers’ regulatory assets fell from $297M (May 2021) to $110M (September 2026); clients rose from 11 to 16 and employees fell from 6 to 4.
Figures from each annual filing
| Filed | Regulatory AUM | Clients | Employees | Offices |
|---|---|---|---|---|
| September 2026 | $110M | 16 | 4 | 1 |
| April 2025 | $201M | 15 | 5 | 1 |
| July 2024 | $245M | 9 | 6 | 1 |
| April 2023 | $296M | 13 | 5 | 1 |
| March 2022 | $435M | 16 | 5 | 1 |
| May 2021 | $297M | 11 | 6 | 1 |
Besides its headquarters, Mainline Investment Advisers has 0 offices, with 1 listed address in Pennsylvania.
Pennsylvania · 1 listed address
- 308 E. Lancaster Avenue, Suite 300, WynnewoodHQ
Other business names
Mainline Investment Advisers has reported 2 other business names to the SEC.
- Mainline Companies
- Mainline Investments
Contact and registration details
- Legal name
- Mainline Investment Advisers, LLC
- Headquarters
- 308 E. Lancaster Avenue, Suite 300, Wynnewood, PA 19096-2145
- Website
- mainlineco.com
- Phone
- 610-896-3000
- @mainline-investment-advisors
- SEC file
- 801-72761
- Structure
- Delaware LLC
- Fiscal year end
- December
Mainline Investment Advisers has custody of $28.8M in client assets for 6 clients.
What the accounts hold
- Other100%
- Privately-issued securities obtained in a private placement (securities that are acquired from the issuer in transaction(s) not involving a public offering; uncertificated and ownership thereof is recorded only on the books of the issuer in name of the client; and transferable only with the prior consent of the issuer.)100%
How many clients does Mainline Investment Advisers have?
Mainline Investment Advisers has 16 clients and manages $110 million for them, as of September 2026. They include 9 pooled investment vehicles and 7 high-net-worth individuals.
Source: Form ADV Part 1A, Items 5.D and 5.F, filed 1 September 2026
What services does Mainline Investment Advisers offer?
Mainline Investment Advisers provides portfolio management for individuals and small businesses and portfolio management for pooled vehicles.
Source: Form ADV Part 1A, Item 5.G, from the SEC's 2 October 2026 data file
How many financial advisors does Mainline Investment Advisers have?
Mainline Investment Advisers has 2 investment adviser representatives registered with state securities authorities, out of 4 employees, and 3 perform investment advisory functions. 1 employee is a registered representative of a broker-dealer and 1 employee is a licensed insurance agent.
Source: Form ADV Part 1A, Items 5.A and 5.B, from the SEC's 2 October 2026 data file
What does Mainline Investment Advisers invest in?
At the end of its last fiscal year, Mainline Investment Advisers’ separately managed accounts held 100% other. The 100% other category is described as: Privately-Issued Securities Obtained in A Private Placement (Securities That Are Acquired From the Issuer in Transaction(s) Not Involving A Public Offering; Uncertificated and Ownership Thereof Is Recorded Only on the Books of the Issuer in Name of the Client; and Transferable Only With the Prior Consent of the Issuer.). It advises 8 private funds.
Source: Form ADV Part 1A, Items 5.K.(1) and 7.B, from the SEC's 2 October 2026 data file
Who owns Mainline Investment Advisers?
Mainline Investment Advisers is owned through a holding company by William Landman and David Clapper. Its direct owner is Mainline Investment Partners, LLC (75% or more).
Source: Form ADV Part 1A, Schedules A and B, filed 1 September 2026
How does Mainline Investment Advisers get paid?
Mainline Investment Advisers is paid through a percentage of assets under management, fixed fees, performance-based fees and other compensation. Its Form ADV lists no commissions among how it is paid.
Source: Form ADV Part 1A, Item 5.E, from the SEC's 2 October 2026 data file
How do I contact Mainline Investment Advisers?
Mainline Investment Advisers’ main office is at 308 E. Lancaster Avenue, Suite 300, Wynnewood, PA 19096-2145. Its phone number is 610-896-3000. Its website is mainlineco.com.